return of the coral reef hypothesis basin to shelf partitioning of caco3 and its effect on atmospheric co2 differences in the rate of coral reef carbonate deposition from the pleistocene to the holocene may account for the quaternary variation of atmospheric co sub 2 volumes of carbonate associated with holocene reefs require an average deposition rate of 2 0 times 10 sup 13 mol yr for the past 5 ka in light of combined riverine mid ocean ridge and ground water fluxes of calcium to the oceans of 2 3 times 10 sub 13 mol yr the current flux of calcium carbonate to pelagic sediments must be far below the pleistocene average of 1 2 times 10 sub 13 mol yr the authors suggest that sea level change shifts the locus of carbonate deposition from the deep sea to the shelves as the normal glacial interglacial pattern of deposition of quaternary global carbonates to assess the impact of these changes on atmospheric co sub 2 a simple numerical simulation of the global carbon cycle was developed atmospheric co sub 2 as well as calcite saturation depth and sediment responses to these carbonate deposition changes are examined atmospheric co sub 2 changes close to those observed in the vostok ice core approximately 80 ppm co sub 2 for the quaternary are observed as well as the approximate depth changes in percent carbonate of sediments measured in themore pacific ocean over the same time interval less

the role of caco3 compensation in the glacial to interglacial atmospheric co2 change the only viable explanations put forth to date for the glacial to interglacial change in atmospheric co2 content suggested from measurements of the co2 content of gas extracted from ice cores involve changes in the ocean s nutrient cycles any nutrient change capable of creating the 80 atm changes in atmosphere co2 pressure suggested by the ice core results also creates significant change in the deep ocean s co3 content evidence from deep sea sediments suggests that these co3 changes are compensated on the time scale of a few thousand years by reductions or increases in amount of caco3 accumulating in deep sea sediments this compensation process has two important consequences first it significantly increases the magnitude of the co2 change per unit of nutrient forcing second it causes a delay in the response of the atmospheric co2 change while the first of these consequences is a boon to those seeking to explain the co2 change the second may prove to be a curse the ice core co2 record shows no evidence of a significant lag between the co2 response and the polar warming in any case it is important that we improve our knowledge of the magnitude and timing of the caco3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

neritic and pelagic carbonate sedimentation in the marine environment ignorance is not bliss synthesis of available data allows us to define general patterns of late quaternary carbonate production and sedimentation in the global ocean during high stands of sea level the neritic and pelagic environments appear to sequester approximately similar amounts of carbonate whereas during low stands of sea level the decreased neritic zone produces and accumulates approximately an order of magnitude less carbonate assuming that global accumulation of deep sea carbonates remains more or less constant during glacially induced changes in sea level the ocean becomes depleted with respect to calcium carbonate during high stands and recharges during low stands before we can achieve a better understanding of the global carbonate system however we need a better understanding of key environments and processes a production and accumulation on continental shelves both as potential sinks accumulation and as sources export to the deep sea b a better measure of pelagic carbonate production and c late quaternary late pleistocene and holocene mass accumulation rates in the deep sea

an investigation of disequilibrium growth processes of plagioclase in the system anorthite albite water by methods of numerical simulation compositional zoning of plagioclase is useful as a recorder of dynamic geological conditions if the mechanisms of crystal growth are known although the present lack of quantitative information on specific kinetic processes limits their accuracy numerical simulations of phenoycryst plagioclase growth are useful both for identifying the most influential kinetic processes for example diffusion that should receive priority in experimental measurements and for designing informative growth experiments the interaction of kinetic processes at a crystal face is so complex that the overall result cannot be assessed intuitively a primary purpose of these papers is to explore this interaction in the plagioclase system as quantitatively as data permit

ocean thermohaline circulation and sedimentary 231pa 230th ratio holocene sediments from the atlantic are characterized by 231pa 230th ratios below the production ratio of the two radionuclides in the water column 0 093 whereas holocene sediments from the southern ocean have 231pa 230th 0 093 this pattern of 231pa deficit and excess was ascribed to southward 231pa export from the atlantic by the atlantic thermohaline circulation thc as pa is scavenged less efficiently by marine particles and more effectively transported by the thc than th the same pattern is observed in deposits of the last glacial maximum lgm which led to a previous contention that the thc strength did not vary markedly through the last glacial termination here we embed a description of trace metal scavenging into a zonally averaged circulation biogeochemistry ocean model to explore the sensitivity of 231pa 230th in atlantic and southern ocean sediments to thc changes our results show that the production of biogenic opal which unlike other marine particles poorly fractionates th and pa in the southern ocean water column determines the spatial pattern of the sensitivity also 231pa 230th increases in the north atlantic but changes little in the south atlantic and decreases in the southern ocean as thc is reduced the mean 231pa 230th of the whole atlantic is therefore less sensitive to thc changes than the mean 231pa 230th of the north atlantic the current uncertainties in atlantic mean 231pa 230th are too large to rule out a twofold reduction of the thc at the lgm however the increase in north atlantic mean 231pa 230th simulated in response to a twofold thc reduction is larger than the observed change in the north atlantic mean 231pa 230th from the lgm to holocene comparing this change with the modeled sensitivity of north atlantic 231pa 230th to thc variations indicates that the thc at the lgm could not have been reduced by 30 of its present strength experiments of transient thc changes indicate that high resolution 231pa 230th records from north atlantic sediments could also document thermohaline oscillations on century to millennial timescales

glacial to holocene redistribution of carbonate ion in the deep sea we have reconstructed the glacial age distribution of carbonate ion concentration in the deep waters of the equatorial ocean on the basis of differences in weight between glacial and holocene foraminifera shells picked from a series of cores spanning a range of water depth on the western atlantic s ceara rise and the western pacific s ontong java plateau the results suggest that unlike today s ocean sizable vertical gradients in the carbonate ion concentration existed in the glacial age deep ocean in the equatorial pacific the concentration increased with depth and in the atlantic it decreased with depth in addition the contrast between the carbonate ion concentration in deep waters produced in the northern atlantic and deep water in the pacific appears to have been larger than in today s ocean

the mystery of the missing deglacial carbonate preservation maximum abstract a leading hypothesis for lower atmospheric co 2 levels during glacial periods invokes increased ocean stratification with a corresponding shift of dissolved inorganic carbon and nutrients from intermediate depths to deep waters if the rapid deglacial rise in atmospheric co 2 17 10 ka were caused by a breakdown of this stratification and increased ventilation of deep water masses then one consequence would be increased caco 3 preservation in deep sea sediments we present down core records of caco 3 preservation for the last 21 000 years from 31 cores in the tropical and subtropical pacific atlantic and indian oceans our preservation records are based on a multi proxy approach involving a new caco 3 dissolution proxy the globorotalia menardii fragmentation index size normalized foraminifer shell weights and 230 th normalized caco 3 accumulation rates in some cores our proxy records add to the growing body of evidence in support of the hypothesized breakdown of glacial stratification however in most cores the expected deglacial increase in caco 3 preservation is missing accepting that the deglacial hypothesis is well supported by other evidence here we explore processes and conditions that erased the expected caco 3 signal from our records including 1 variations in the ratio of organic carbon to caco 3 flux in the eastern equatorial pacific 2 very low sedimentation rates and bioturbation in the western equatorial pacific and 3 increased northward penetration of antarctic bottom water in the equatorial atlantic

sequestration of carbon in the deep atlantic during the last glaciation atmospheric co2 concentrations declined markedly about 70 000 years ago when the earth s climate descended into the last glaciation much of the carbon removed from the atmosphere has been suspected to have entered the deep oceans but evidence for increased carbon storage remains elusive here we use the b ca ratios of benthic foraminifera from several sites across the atlantic ocean to reconstruct changes in the carbonate ion concentration and hence the carbon inventory of the deep atlantic across this transition we find that deep atlantic carbonate ion concentration declined by around 25 mol kg 1 between 80 000 and 65 000 years ago this drop implies that the deep atlantic carbon inventory increased by at least 50 gt around the same time as the amount of atmospheric carbon dropped by about 60 gt from a comparison with proxy records of deep circulation and climate model simulations we infer that the carbon sequestration coincided with a shoaling of the atlantic meridional overturning circulation we thus conclude that changes in the atlantic ocean circulation may have played an important role in reductions of atmospheric co2 concentrations during the last glaciation by increasing the carbon storage in the deep atlantic

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

modeling the response of the oceanic si inventory to perturbation and consequences for atmospheric co2 1 it has been suggested that much of the observed glacial interglacial variability in the atmospheric mixing ratio of co2 xco2 could potentially be driven by a perturbation of the marine si cycle to date only relatively simple steady state analysis has been made of this hypothesis in this study we develop a description of the ocean carbon cycle incorporating novel descriptions for the recycling of si both within the water column and in deep sea sediments a high degree of computational efficiency enables model integrations over multiple glacial interglacial cycles driven by a time varying input of dissolved si to the ocean due to the long time constant 23 ka of atmospheric xco2 response to perturbation in si supply and the highly nonlinear nature of opal preservation in deep sea sediments we find that reduction in the deposition rate of aeolian silicates at the surface ocean can explain little 3 ppm of the rapid 90 ppm rise in atmospheric xco2 observed at glacial termination however increased si supply has the potential to make an important contribution to the decline in atmospheric xco2 associated with the much slower transition from interglacial to full glacial conditions

toward explaining the holocene carbon dioxide and carbon isotope records results from transient ocean carbon cycle climate simulations records of atmospheric co2 and d 13 c as well as the spatiotemporal evolution of d 13 c and carbonate ion concentration in the deep sea deposition of shallow water carbonate carbonate compensation of land uptake during the glacial termination land carbon uptake and release during the holocene and the response of the ocean sediment system to marine changes during the termination contribute roughly equally to the reconstructed late holocene pco2 rise of 20 ppmv the 5 ppmv early holocene pco2 decrease reflects terrestrial uptake largely compensated by carbonate deposition and ocean sediment responses additional small contributions arise from holocene changes in sea surface temperature ocean circulation and export productivity the holocene pco2 variations result from the subtle balance of forcings and processes acting on different timescales and partly in opposite direction as well as from memory effects associated with changes occurring during the termination different interglacial periods with different forcing histories are thus expected to yield different pco2 evolutions as documented by ice cores

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

implications of coral reef buildup for the controls on atmospheric co2 since the last glacial maximum we examine the effect on atmospheric co2 of the occurrence of increased shallow water carbonate deposition and regrowth of the terrestrial biosphere following the last glacial we find that contrary to recent speculations that changes in terrestrial carbon storage were primarily responsible for the observed similar to20 ppmv late holocene co2 rise a more likely explanation is coral reef buildup and other forms of shallow water carbonate deposition during this time the importance of a responsive terrestrial carbon reservoir may instead be as a negative feedback restricting the rate of co2 rise possible in the early stages of the deglacial transition this separation in time of the primary impacts of regrowth of the terrestrial biosphere and increased shallow water carbonate deposition explains the occurrence of an early holocene carbonate preservation event observed in deep sea sediments we demonstrate that their combined influence is also consistent with available proxy estimates of deep ocean carbonate ion concentration changes over the last 21 kyr accounting for the processes that act on the carbonate chemistry of the ocean as a whole then allows us to place strong constraints on the nature of the remaining processes that must be operating at the deglacial transition by subtracting the net co2 effect of coral reef buildup and terrestrial biosphere regrowth from recent high resolution ice core data we highlight two periods from 17 0 to 13 8 kyr and 12 3 to 11 2 kyr bp characterized by sustained rapid rates of co2 increase 12 ppmv kyr 1 because these periods are coincident with southern hemisphere deglaciation we argue that changes in the biogeochemical properties of the southern ocean surface are the most likely cause

the δ18o of atmospheric o2 from air inclusions in the vostok ice core timing of co2 and ice volume changes during the penultimate deglaciation one important question about the co2 climate connection is how increasing atmospheric pco2 levels affect climate and thereby the mass balance of continental ice sheets a record of atmospheric co2 variations over the last 160 000 years has recently been constructed by analyzing the trapped gas in the vostok ice core barnola et al 1987 the relationship between changes in atmospheric co2 and the size of the continental ice sheets has been difficult to ascertain because the co2 record is obtained from ice cores while the ice volume record has been constructed from the stable isotopic composition of biogenic caco3 in deep sea sediment cores in order to compare these two records in a more precise manner we present a record of the isotopic composition 18o of atmospheric o2 trapped in the vostok ice core and propose that it may be considered a proxy for the 18o of seawater and hence ice volume having a record of atmospheric co2 along with a continental ice volume proxy in trapped air in the same ice core allows us to compare the timing of changes in these two parameters with little uncertainty in the relative ages of important events our results suggest that during the penultimate glacial termination atmospheric co2 began to increase at least 3 kyr before the initial introduction of meltwater to the oceans possible errors in the relative age depth curve of the vostok ice core and uncertainties in the influence of biological and hydrologic processes on the 18o of atmospheric o2 introduce some uncertainty into our conclusions however our results are in general agreement with the observed phase relationship between atmospheric co2 and ice volume imbrie et al 1984 imbrie et al 1989 inferred from changes in the 13c difference between contemporaneous planktonic and benthic forams deposited in deep sea cores and the specmap ice volume record

the challenge of modeling interglacial co2 and ch4 trends abstract a vigorous debate about the early anthropogenic explanation of greenhouse gas increases in the late holocene has been underway for years but what about the current status of natural explanations for the gas trends modelers have called on a wide range of natural factors to explain the holocene gas increases but have not yet converged on an explanation no model has yet reproduced both the upward gas trends during the holocene and the downward gas trends during previous interglaciations

high resolution holocene n2o ice core record and its relationship with ch4 and co2 1 nitrous oxide n 2 o concentration records exist for the last 1000 years and for time periods of rapid climatic changes like the transition from the last glacial to today s interglacial and for one of the fast climate variations during the last ice age little is known however about possible n 2 o variations during the more stable climate of the present interglacial holocene spanning the last 11 thousand years here we fill this gap with a high resolution n 2 o record measured along the european project for ice coring in antarctica epica dome c antarctic ice core on the same ice we obtained high resolution methane and carbon dioxide records this provides the unique opportunity to compare variations of the three most important greenhouse gases after water vapor without any uncertainty in their relative timing the co 2 and ch 4 records are in good agreement with previous measurements on other ice cores the n 2 o concentration started to decrease in the early holocene and reached minimum values around 8 ka 260 ppbv before a slow increase to its preindustrial concentration of 265 ppbv

responses of the deep ocean carbonate system to carbon reorganization during the last glacial interglacial cycle we present new deep water carbonate ion concentration co 3 2 records reconstructed using cibicidoides wuellerstorfi b ca for one core from caribbean basin water depth 3623 m sill depth 1 8 km and three cores located at 2 3 4 3 km water depth from the equatorial pacific ocean during the last glacial interglacial cycle the pattern of deep water co 3 2 in the caribbean basin roughly mirrors that of atmospheric co 2 reflecting a dominant influence from preformed co 3 2 in the north atlantic ocean compared to the amplitude of 65 mol kg in the deep caribbean basin deep water co 3 2 in the equatorial pacific ocean has varied by no more than 15 mol kg due to effective buffering of caco 3 on deep sea ph in the pacific ocean our results suggest little change in the global mean deep ocean co 3 2 between the last glacial maximum lgm and the late holocene the three records from the pacific ocean show long term increases in co 3 2 by 7 mol kg from marine isotope stage mis 5c to mid mis 3 consistent with the response of the deep ocean carbonate system to a decline in neritic carbonate production associated with 60 m drop in sea level the coral reef hypothesis superimposed upon the long term trend deep water co 3 2 in the pacific ocean displays transient changes which decouple with 13 c in the same cores at the start and end of mis 4 these changes in co 3 2 and 13 c are consistent with what would be expected from vertical nutrient fractionation and carbonate compensation the observed 4 mol kg co 3 2 decline in the two pacific cores at 3 4 km water depth from mis 3 to the lgm indicate further strengthening of deep ocean stratification which contributed to the final step of atmospheric co 2 drawdown during the last glaciation the striking similarity between deep water co 3 2 and 230 th normalized caco 3 flux at two adjacent sites from the central equatorial pacific ocean provides convincing evidence that deep sea carbonate dissolution dominantly controlled caco 3 preservation at these sites in the past our results offer new and quantitative constraints from deep ocean carbonate chemistry to understand roles of various mechanisms in atmospheric co 2 changes over the last glacial interglacial cycle

deglacial co2 buildup constraints on the coral reef model abstract the coral reef hypothesis of degalcial co2 buildup in the atmosphere can account for about one half of the signal seen in ice cores assuming additional coral reef growth releases 2 atmospheric carbon masses acm the carbonate dissolution signal on the deep sea floor suggest titration of only 1 acm at least 4 acm of co2 must be made available to satisfy the requirements of pco2 increases growth of biosphere and of sedimentary carbon pool carbonate dissolution on the sea floor and saturation of newly introduced meltwater a drop in ocean fertility is called for to provide the missing co2 such a drop is evident in deep sea cores from the western equatorial pacific co2 buildup appears to occur as a step near 13 500 years b p dissolution on the deep sea floor begins near 11 000 years b p the difference of 2500 years may describe a mixing lag due to meltwater input the worthington effect

understanding the causes and consequences of past marine carbon cycling variability through models abstract on geological time scales the production and degree of recycling of biogenic carbon in the marine realm and ultimately its removal to sediments exerts a dominant control on atmospheric co 2 and hence variability in climate this is a highly complex system involving a myriad of inter connected biological chemical and physical processes for this reason alone linking observations often highly abstracted in the form of proxies to the primary processes involved and ultimately to explanatory hypotheses for specific geological events and transitions is challenging the past few decades have seen a progressive improvement in theoretical and process based understanding of the various components that make up the marine carbon cycle and hand in hand with this the development of numerical model representations of the complete system models have also been designed and or adapted with paleoclimate questions in mind and applied to quantitatively explore the role of the marine carbon cycle in both perturbations and long term geologic evolutionary trends in global climate and possible feedbacks between them however we must ask whether paleoclimate models incorporate sufficiently appropriate representations of the dynamics and sensitivities of the marine carbon cycle and indeed whether in the geological context we really know what these dynamics are here we provide a comprehensive overview of how marine carbon cycling and the biological carbon pump is treated in available paleoclimate models with the aim of critically evaluating their ability to help interpret past marine carbon cycle and climate dynamics to this end we first provide an overview of commonly used paleoclimate models and some of their associated paleo applications drawing from a wide range of global carbon cycle box models and earth system models of intermediate complexity emics secondly we review and evaluate the three dominant processes involved in the cycling of organic and inorganic carbon in the marine system and how they are represented in models namely biological productivity at the ocean surface remineralisation dissolution of particulate carbon within the water column and the benthic pelagic coupling at the seafloor we generate and employ illustrative examples using the model genie to show how different parameterisations of water column and sediment processes can lead to significantly different model projections our compilation reveals the prevalence of static parameterisations of marine carbon cycling among existing paleoclimate models which are commonly empirically derived from present day observations although such approaches tend to represent carbon transfer in the modern ocean well they are potentially compromised in their ability to reflect the true degree of freedom and strength of feedbacks with respect to past climate events particularly those characterised by environmental boundary conditions that differ fundamentally from today finally we discuss the importance of using models of different complexities and how questions of model uncertainty may start to be addressed

holocene carbon cycle dynamics 1 we are investigating the late holocene rise in co2 by performing four experiments with the climate carbon cycle model climber2 lpj apart from the deep sea sediments important carbon cycle processes considered are carbon uptake or release by the vegetation carbon uptake by peatlands and co2 release due to shallow water sedimentation of caco3 ice core data of atmospheric co2 between 8 ka bp and preindustrial climate can only be reproduced if co2 outgassing due to shallow water sedimentation of caco3 is considered in this case the model displays an increase of nearly 20 ppmv co2 between 8 ka bp and present day model configurations that do not contain this forcing show a slight decrease in atmospheric co2 we can therefore explain the late holocene rise in co2 by invoking natural forcing factors only and anthropogenic forcing is not required to understand preindustrial co2 dynamics

glacial interglacial variability of atmospheric co2 due to changing continental silicate rock weathering a model study an 11 box model of the oceanic carbon cycle including sedimentary processes is used to explore the role chemical weathering of continental silicate rocks might play in driving atmospheric co2 levels on glacial interglacial timescales histories for the consumption of co2 by silicate rock weathering processes are derived from the marine ge si record taking the major uncertainties in the knowledge of the ge and si cycles into account several histories for the evolution of the riverine dissolved silica fluxes are calculated from this record the investigation of the systematics between riverine dissolved silica and bicarbonate fluxes under different weathering regimes leads us to the tentative conclusion that although there is no correlation between dissolved silica and total bicarbonate concentrations in the major rivers there may exist a negative correlation between weathering intensity and the ratio of dissolved silica to bicarbonate derived from silicate weathering alone with this correlation as a working hypothesis it is possible to interpret the dissolved silica fluxes in terms of equivalent co2 consumption rates the calculated histories indicate that glacial rates of co2 consumption by chemical silicate rock weathering could have been twice and possibly up to 3 5 times as high as they are today when used to force the carbon cycle model they are responsible for glacial interglacial pco2 variations in the atmosphere of typically 50 60 ppm and up to 95 110 ppm these variations are superimposed to a basic oscillation of 60 ppm generated by the model mainly in response to coral reef buildup and erosion processes the total pco2 signal has an amplitude of about 80 90 ppm and up to 125 135 ppm although these large amplitudes indicate that silicate weathering processes should be taken into account when studying glacial interglacial changes of co2 in the atmosphere it also raises new problems such as too high co2 levels during the period from 110 70 kyr b p requiring further study

caco3 size distribution a paleocarbonate ion proxy lysocline reconstructions play an important role in scenarios purporting to explain the lowered atmospheric co2 content of glacial time these reconstructions are based on indicators such as the caco3 content the percent of coarse fraction the ratio of fragments to whole foraminifera shells the ratio of solution susceptible to solution resistant species and the ratio of coarse to fine caco3 all assume that changes with time in the composition of the input material do not bias the result however as the composition of the input material does depend on climate none of these indicators provides an absolute measure of the extent of dissolution in this paper we evaluate the reliability of the ratio of 63 m caco3 to total caco3 as a dissolution indicator we present here results that suggest that in today s tropics this ratio appears to be determined solely by co3 ion concentration and water depth i e the saturation state of bottom waters this finding offers the possibility that the size fraction index can be used to reconstruct co3 ion concentrations for the late quaternary ocean to an accuracy of 5 mol kg 1

covariability of the southern westerlies and atmospheric co2 during the holocene a suite of mechanisms has been proposed to account for natural variations in atmospheric co 2 during the holocene all of which have achieved limited success in reproducing the timing direction and magnitude of change recent modeling studies propose that changes in the latitudinal position and strength of the southern hemisphere westerly winds sww can greatly influence large scale ocean circulation and degassing of the deep ocean via changes in wind driven upwelling in the southern ocean the extent to which the hypothesized sww southern ocean coupled system could account for changes in atmospheric co 2 is uncertain because of a lack of observations on the behavior of the sww in the past the paucity of appropriate records of productivity changes in the southern ocean and our limited understanding of the sensitivity of the southern ocean biological and or physical system to sww forcing here we report a reconstruction of the behavior of the sww during the past 14 k y based on terrestrial ecosystem proxies from western patagonia south america the reconstructed variations in the intensity of zonal flow correspond to the timing and structure of atmospheric co 2 changes and are consistent with the modeled magnitude of co 2 changes induced by varying strengths of the sww the close match between data and models supports the view that the sww southern ocean coupled system underpins multimillennial co 2 variations during the current interglacial and possibly during glacial cycles over the past 800 k y

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

deep pacific caco 3 compensation and glacial interglacial atmospheric co 2 abstract benthic foraminiferal 13c suggests that there was a net shift of isotopically light metabolic co2 from the upper ocean into the deep ocean during the last glacial period according to the caco3 compensation hypothesis this should have caused a transient drop in deep ocean co32 that was eventually reversed by seafloor dissolution of caco3 the resulting increase in whole ocean ph may have had a significant impact on atmospheric co2 compounding any decrease that was due to the initial vertical co2 shift the opposite hypothetically occurred during deglaciation when co2 was returned to the upper ocean and atmosphere and deep ocean co32 temporarily increased followed by excess burial of caco3 and a drop in whole ocean ph the deep sea record of caco3 preservation appears to reflect these processes with the largest excursion during deglaciation as expected but various factors make quantification of deep sea paleo co32 difficult here we reconstruct deep equatorial pacific co32 over the last glacial interglacial cycle using benthic foraminiferal zn ca which is strongly affected by saturation state during calcite precipitation our data are in agreement with the caco3 compensation theory including glacial co32 concentrations similar to or slightly lower than today and a termination i co32 peak of 25 30 mol kg 1 the deglacial co32 rise precedes ice sheet melting consistent with the timing of the atmospheric co2 rise a later portion of the peak could reflect removal of co2 from the atmosphere ocean system due to boreal forest regrowth caco3 compensation alone may explain more than one third of the atmospheric co2 lowering during glacial times

abrupt climate induced changes in carbonate burial in the arabian sea causes and consequences we present high resolution records of aragonite contents and pteropods abundance in two sediment cores sk 17 and md 76 131 within the oxygen minimum zone omz of the eastern arabian sea we show large increases in aragonite contents during glacial and particularly during stadials heinrich events using aragonite content pteropods abundance organic carbon percentage and abundance of fertile species of planktonic foraminifer we demonstrate that aragonite contents in the eastern arabian sea primarily reflects preservation linked to the deepening of aragonite compensation depth acd in the arabian sea we show that these aragonite preservation events correspond with time equivalents of henrich events when arabian sea experienced large declines in monsoon driven productivity and greater penetration of antarctica intermediate water aaiw into the arabian sea thus pteropod preservation in the arabian sea appears to be the result of rapid climate change through atmospheric and oceanic teleconnections we suggest that the role of aragonite carbonate production and burial in margins and the resultant co2 climate feedback to rapid climate changes remains poorly constrained

a search for an early holocene caco3 preservation event the co2 record for air bubbles from the byrd station ice core suggest a drawdown in the ocean atmosphere carbon reservoir during the early holocene such a drawdown would require a corresponding increase in the co3 ion concentration in the deep sea we report here the results of a search in atlantic sediments for evidence that the lysocline showed a corresponding deepening while both the pteropod and the calcite preservation records we have obtained are consistent with expectation they are not conclusive

dust impact on marine biota and atmospheric co2 during glacial periods 1 we assess the impact of high dust deposition rates on marine biota and atmospheric co2 using a state of the art ocean biogeochemistry model and observations our model includes an explicit representation of two groups of phytoplankton and colimitation by iron silicate and phosphate when high dust deposition rates from the last glacial maximum lgm are used as input our model shows an increase in the relative abundance of diatoms in today s iron limited regions causing a global increase in export production by 6 and an atmospheric co2 drawdown of 15 ppm when the combined effects of changes in dust temperature ice cover and circulation are included the model reproduces roughly our reconstruction of regional changes in export production during the lgm based on several paleoceanographic indicators in particular the model reproduces the latitudinal dipole in the southern ocean driven in our simulations by the conjunction of dust sea ice and circulation changes in the north pacific the limited open ocean data suggest that we correctly simulate the east west gradient in the open ocean but more data are needed to confirm this result from our model data comparison and from the timing of the dust record at vostok we argue that our model estimate of the role of dust is realistic and that the maximum impact of high dust deposition on atmospheric co2 must be 30 ppm

orbital changes and climate at the 41 000 period of orbital tilt summer insolation forces a lagged response in northern ice sheets this delayed ice signal is rapidly transferred to nearby northern oceans and landmasses by atmospheric dynamics these ice driven responses lead to late phased changes in atmospheric co2 that provide positive feedback to the ice sheets and also project late 41 k forcing across the tropics and the southern hemisphere responses in austral regions are also influenced by a fast response to summer insolation forcing at high southern latitudes at the 22 000 year precession period northern summer insolation again forces a lagged ice sheet response but with muted transfers to proximal regions and no subsequent effect on atmospheric co2 most 22 000 year greenhouse gas responses have the early phase of july insolation july forcing of monsoonal and boreal wetlands explains the early ch4 response the slightly later 22 k co2 response originates in the southern hemisphere the early 22 k ch4 and co2 responses add to insolation forcing of the ice sheets the dominant 100 000 year response of ice sheets is not externally forced nor does it result from internal resonance internal forcing appears to play at most a minor role the origin of this signal lies mainly in internal feedbacks co2 and ice albedo that drive the gradual build up of large ice sheets and then their rapid destruction ice melting during terminations is initiated by uniquely coincident forcing from insolation and greenhouse gases at the periods of tilt and precession

rapid changes in ocean circulation and atmospheric radiocarbon a latitude depth coupled global ocean ice atmosphere model is extended to include a simple biosphere component a physically reasonable adjustment of runoff into the north atlantic is invoked to achieve a transient response to glacial meltwater perturbations which closely resembles the younger dryas climate event we then investigate the evolution of the isotopic ratio of atmospheric radiocarbon 14c due to the rapid changes of deep ocean circulation when the north atlantic branch of the conveyor belt circulation is interrupted the oceanic uptake of radiocarbon is reduced resulting in an increase of atmospheric 14c by about 35 the reduction of ventilation in the north atlantic is partly compensated by an increase of the 14c ratios of the biosphere the southern ocean and the upper ocean above 1000 m depth a plateau of the 14c year calendar year relation can be generated at the time of the rapid reinitiation of deep ocean ventilation which begins coincident with the major temperature increase and lasts for about 60 years it is hence significantly shorter than that found by analyzing tree rings during the termination of younger dryas longer than 400 years a sensitivity study reveals that the duration of the plateau depends strongly on the transient evolution of the gas exchange rate and can increase to 150 300 years if changes of pco2 or sea ice coverage are taken into account

model limits on the role of volcanic carbon emissions in regulating glacial interglacial co2 variations abstract huybers and langmuir 2009 proposed that an increase in volcanic activity provoked by ice sheet melting contributed substantially to the deglacial co 2 increase here their hypothesis is evaluated by prescribing their central high and low volcanic co 2 emission scenarios in the bern3d carbon cycle climate model as a perturbation reconstructed emissions increase mainly between 15 and 11 ka bp remain high in the early holocene and drop after 7 ka bp in all scenarios with total emissions between 181 and 2011 gtc simulated increase of atmospheric co 2 peaks around 6 ka bp at 46 ppm for the central scenario and with a range between 13 and 142 ppm modeled carbonate ion concentration in the deep ocean decreases and the calcite saturation horizon shoals on global average by 440 m 150 to 1500 m simulated changes in 13 c and 14 c isotopic signatures are small compared to reconstructed proxy based changes over the deglacial period the comparison of our model results and available proxy evidence suggests a small role for volcanic carbon emissions in regulating glacial interglacial co 2 variations but uncertainties prevent a firm conclusion a problem with the volcanic emission hypothesis is in the timing of emissions which peak in the early holocene a period of decreasing atmospheric co 2

wobbly ocean conveyor circulation during the holocene abstract compared to the last glacial period the climate of the holocene has been quite stable however the record does suggest that at high latitudes in the north temperatures have cooled at least since the middle holocene and that this cooling has been modulated by millennial duration fluctuations that culminated in the medieval warm little ice age oscillation in this paper we explore the possibility that these variations were associated with concurrent changes in the strength of the atlantic s conveyor circulation three lines of evidence are considered one involves records that relate directly to ocean operation a second involves the tie between sea ice extent in the northern atlantic and the extent of mountain glaciers in the european alps and in the cordillera of western north america and a third involves evidence for a bipolarity in climate changes in the northern and southern polar regions in addition we look into clues provided by the atlantic multidecadal oscillation amo although at this point no firm conclusion can be drawn the case for ocean involvement is sufficiently strong to merit further attention

sundaland peat carbon dynamics and its contribution to the holocene atmospheric co2 concentration the sunda shelf is a large submerged extension of the continental shelf of mainland asia joining the islands of borneo java and sumatra and forming the shallow seabed of the south china sea recent studies identified present day peatlands in southeast asia as a globally important carbon reservoir however little is known about sundaland paleo peatlands and their role in the global carbon cycle since the last glacial maximum using a topography based sea level driven model we estimate the potential spatial extent of peatlands during the late pleistocene and early holocene across the low lying sundaland plains we then use the estimated peatland area together with data on carbon accumulation rates to calculate the total peat carbon pool on the sunda shelf finally using a global biogeochemical model we analyze the relative influence of the predicted sundaland peat dynamics and other carbon change mechanisms specifically high latitude forest growth and peat formation shallow sea carbonate deposition ocean warming and combinations of them on the global carbon cycle of the holocene we identify a feedback mechanism between sea level and peatland carbon sequestration in sundaland that reduced atmospheric co2 concentration by about 4 5 ppm and increased 13c by 0 05 during the holocene we also show that a concurrence of mechanisms that includes sundaland peat dynamics produces model results that are consistent with proxy records especially with respect to 13c

strontium diffusion kinetics in plagioclase feldspars abstract a pronounced systematic variation by a factor of 104 in strontium tracer diffusion kinetics has been measured in four feldspar specimens that span the range of plagioclase compositions the experiments were carried out in air using isotopically enriched 86sr and analyzed with an ion microprobe the arrhenius relations for strontium diffusion are plagioclase ab d 0 m 2 s q kj g atom sr temperature range c albite 98 1 05e 279 550 1080 oligoclase 73 7 4e 7 261 750 1100 labradorite 36 1 1e 6 295 800 1300 anorthite 4 5 7e 9 267 900 1300 no difference was found within the measurement uncertainty between these results and those for albite under hydrothermal conditions at one kbar 100 mpa strontium diffusion rates parallel to and normal to the albite twin lamellae are the same there is no effect on the strontium diffusion rate in albite between an oxygen partial pressure of 0 2 bar air and 10 19 bar graphite buffer a relation is developed that permits calculation of the strontium diffusion arrhenius parameters for any normal plagioclase composition the large variation in diffusion rate with composition has a major effect on the ease of strontium isotope exchange at high temperatures between plagioclases and coexisting phases in rocks which may prove useful in determining thermal histories

comparative carbon cycle dynamics of the present and last interglacial changes in temperature and carbon dioxide during glacial cycles recorded in antarctic ice cores are tightly coupled however this relationship does not hold for interglacials while climate cooled towards the end of both the last eemian and present holocene interglacials co2 remained stable during the eemian while rising in the holocene we identify and review twelve biogeochemical mechanisms of terrestrial vegetation dynamics and co2 fertilization land use wildfire accumulation of peat changes in permafrost carbon subaerial volcanic outgassing and marine origin changes in sea surface temperature carbonate compensation to deglaciation and terrestrial biosphere regrowth shallow water carbonate sedimentation changes in the soft tissue pump and methane hydrates which potentially may have contributed to the co2 dynamics during interglacials but which remain not well quantified we use three earth system models esms of intermediate complexity to compare effects of selected mechanisms on the interglacial co2 and 13co2 changes focusing on those with substantial potential impacts namely carbonate sedimentation in shallow waters peat growth and in the case of the holocene human land use a set of specified carbon cycle forcings could qualitatively explain atmospheric co2 dynamics from 8 ka bp to the pre industrial however when applied to eemian boundary conditions from 126 to 115 ka bp the same set of forcings led to disagreement with the observed direction of co2 changes after 122 ka bp this failure to simulate late eemian co2 dynamics could be a result of the imposed forcings such as prescribed caco3 accumulation and or an incorrect response of simulated terrestrial carbon to the surface cooling at the end of the interglacial these experiments also reveal that key natural processes of interglacial co2 dynamics shallow water caco3 accumulation peat and permafrost carbon dynamics are not well represented in the current esms global scale modeling of these long term carbon cycle components started only in the last decade and uncertainty in parameterization of these mechanisms is a main limitation in the successful modeling of interglacial co2 dynamics

plagioclase residence times at two island arc volcanoes kameni islands santorini and soufriere st vincent determined by sr diffusion systematics the diffusive relaxation of trace element profiles in plagioclase phenocrysts may provide important constraints on magma residence times in crustal magma chambers initial trace element profiles in plagioclase phenocrysts are governed by variations in the concentration of a trace element in the melt and by the plagioclase melt partition coefficient trace element diffusion will subsequently act to modify this initial profile and given enough time produce a profile that is in equilibrium with the anorthite variations within the crystal we argue that the trace element partition coefficient da b between two parts a and b of a plagioclase crystal of variable anorthite content is equal to the ratio of their crystal liquid partition coefficients and that the equilibrium profile of the crystal can be calculated the time required to establish diffusive equilibrium is dependent on the wavelength and amplitude of the initial trace element concentration range and on the diffusivity of the trace element in plagioclase strontium plagioclase melt partition coefficients and diffusivities are calculated for a range of magmatic temperatures and plagioclase compositions a one dimensional diffusion model is developed that describes the diffusive destruction of oscillatory trace element zoning with time and allows the calculation of upper limits for plagioclase crystal residence times in a magma reservoir the model is tested using major and trace element concentrations measured along crystal traverses of plagioclase phenocrysts from the kameni island dacites santorini and from the 1979 soufriere andesite st vincent three out of eight plagioclase phenocrysts have sr concentration profiles that are not in diffusive equilibrium for these the diffusion model is employed to calculate maximum crystal residence times from incomplete diffusive equilibration of trace element zoning in plagioclase maximum crystal residence times range from 100 to 450 years this is in good agreement with estimates from crystal size distribution and from ra th disequilibrium studies for the kameni islands for soufriere however such short residence times are incompatible with u th mineral errorchron data that suggest residence times of 40 ka in a thermally buffered magma reservoir to reconcile these apparently different ages we invoke a more complicated magmatic history for soufriere where an initially buffered magma reservoir is disturbed by magma mixing and suffers limited additional crystal fractionation prior to eruption

dissolution origin and syn entrapment compositional change of melt inclusion in plagioclase abstract in the system di ab an h 2 o melt inclusions in plagioclase were reproducibly formed in a series of partial dissolution experiments and the compositional differences from the surrounding matrix melt were evaluated at 200 mpa and 1050 1150 c a seed crystal of an 59 was partially dissolved into the matrix melt which was in equilibrium with more calcic plagioclase than the seed the reaction proceeded inward from the crystal surface by a dissolution and recrystallization process to form a reaction zone composed of melt channels and recrystallized calcic plagioclase the melt channels were choked necked off by the recrystallized plagioclase at the crystal surface to create melt inclusions the experimentally formed inclusions having square and zigzag shapes up to a few tens of micrometers in size are similar in texture to some common types of natural melt inclusion since the partial dissolution of phenocrysts can occur during various magma mixing processes it should be taken into consideration as one of the inclusion formation mechanisms when trying to interpret information from natural melt inclusions especially for those in hydrous arc magmas the chemical composition of the reproduced melt inclusions deviates from the matrix melt basically along the plagioclase liquidus isotherm the molar ratio of ca ca na and the mgo concentration in the synthesized melt inclusion are up to 17 and 61 relative lower than those in the matrix melt respectively this compositional difference is caused by a combination of factors 1 supersaturation with dissolved plagioclase component 2 insufficient diffusive homogenization in the melt channels due to rapid dissolution of plagioclase and 3 the choking off effect on the basis of the experimental results a model for diffusion in a growing melt channel in dissolving plagioclase was constructed which revealed that the concentration of incompatible elements with low diffusivities can be significantly lower in the melt inclusions than that in the matrix melt these results demonstrate the importance of petrography for interpretation of inclusion data and of more experimental studies on melt inclusion origin

mid pleistocene revolution and the eccentricity myth the mid pleistocene revolution mpr is the term used to describe the transition between 41 ka and 100 ka glacial interglacial cycles which occurred about one million years ago despite eccentricity having by far the weakest influence on insolation received at the earth s surface of any of the orbital parameters it is often assumed to be the primary driver of the post mpr 100 ka climate cycles the traditional solution to this is to call for a highly nonlinear response by the global climate system to eccentricity this eccentricity myth is a simplified view of the relationship between global climate and orbital forcing and is in part due to an artefact of spectral analysis our aim here is to clarify the often confused role of eccentricity and review current theories of the mpr we suggest that the post mpr 100 ka glacial interglacial cycles are more closely linked to precession with the saw toothed climate cycles being defined by every four or five precessional cycle because control over the number of precessional cycles involved is determined by eccentricity eccentricity at most paces rather than drives the system if true then one must also question whether the mpr itself defined by an abrupt change in spectral characteristics is not also somewhat misconceived

trace elements in anorthite megacrysts from the kurile island arc a window to across arc geochemical variations in magma compositions abstract anorthite megacrysts from twelve volcanic centers of the kurile island arc were analyzed by the ion microprobe for concentrations of li be b f mg p cl k ti fe co rb sr y zr nb cs ba la ce pr nd sm eu and pb these 1 2 cm megacrysts are mainly found as early phenocrysts in basalts but are also present in andesites rhyolites and hybrid rocks from almost every studied volcanic center both subaerial and submarine electron and ion microprobe studies show that the cores of these megacrysts are homogeneous and unzoned whereas rims often result from overgrowth of sodium richer plagioclase in equilibrium with its host silica richer melt the cores of these megacrysts can be used to see back through fractional crystallization and magma mixing and serve as a window into an earlier basaltic stage of magmatic evolution petrological observations and numerical crystallization modeling indicate that highly anorthitic plagioclase is the first or second after olivine liquidus phase in high al basalts regardless of varying k2o contents across the arc given the narrow compositional range of anorthite megacrysts the across arc chemical variations are well displayed by direct comparison of trace element concentrations in the megacrysts across the arc the concentration of k in megacrysts increases linearly by a factor of 11 ba 13 sr eu 4 be ti p 3 li 2 ree 5 2 whereas concentrations of pb b and halogens and their ratios to hfse either remain constant or decrease with deepening of the benioff zone from 110 to 220 km we used ion microprobe derived plagioclase basalt partition coefficients to convert trace element concentrations in megacrysts to parental magmatic values the reconstructed concentrations of several key trace elements and their correlation with benioff zone depth are consistent with whole rock basalt data but all give systematically more primitive compositions therefore anorthite megacrysts are helpful for retrieving the chemistry of parental basalts which have subsequently suffered variable differentiation and mixing they can be used to assess delicate variations in primary basaltic magma chemistry as a function of benioff zone depth we also report new results for sr nd and pb isotopes for anorthite bearing rocks and other rocks from the same volcanoes across arc zoning with respect to trace element concentrations ratios and isotopic values is largely linear and requires superposition of several petrogenetic processes trace element transfer by fluids variation in degree of partial melting and progressive change of the melting source

holocene carbon cycle dynamics based on co2 trapped in ice at taylor dome antarctica a high resolution ice core record of atmospheric co2 concentration over the holocene epoch shows that the global carbon cycle has not been in steady state during the past 11 000 years analysis of the co2 concentration and carbon stable isotope records using a one dimensional carbon cycle model uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial scale changes of atmospheric co2 concentrations

crystallization and resorption in plutonic plagioclase implications on the evolution of granodiorite magma gesiniec granodiorite strzelin crystalline massif sw poland abstract granodiorite from the gesiniec intrusion strzelin crystalline massif sw poland contains complexly zoned plagioclases five chemically and structurally distinct zones can be correlated among crystals cores 25 35 an inner mantles 40 45 an outer mantles 40 25 an resorption zones 35 50 an and rims 35 30 an good structural and chemical major and trace elements correlation of zones between crystals indicates that zonation was produced by changes in conditions of crystallization on a magma chamber scale plagioclase being the liquidus phase records a time span from the beginning of crystallization to emplacement and rapid cooling of granodiorite as thin dykes crystallization began with the formation of inner mantles the paucity and different sizes of inner mantles suggests slow crystallization in high temperature magma normally zoned inner mantles were formed under increasing undercooling compositional trends in mantles suggest closed system crystallization the major resorption zones were caused by injection of less evolved magma as indicated by the strontium increase in plagioclase the injection triggered a rapid rise of magma and plagioclase crystals facilitating mixing but also inducing fast kinetically controlled growth of complex multiple oscillatory zonation within resorption zones the ascent of magma caused decompression melting of plagioclase and produced melt inclusions within inner mantles the cores the decompression range is estimated at a minimum of 2 kbar emplacement of granodiorite as thin dykes allow rapid cooling and preservation of magmatic zonation in plagioclases melt inclusions crystallized completely during post magmatic cooling the zonation styles of plutonic plagioclase differ markedly from volcanic ones suggesting different magma evolution zones in plutonic plagioclase are well correlated indicating crystallization in quiescent magma where crystals accumulation and compositional magma stratification may occur crystals probably did not travel between different regimes resorption occurred but as single albeit complex episodes good correlation of zones in plutonic plagioclases allows a distinction between the main processes controlling zonation and superimposed kinetic effects

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

implications of the glacial co2 iron hypothesis for quaternary climate change 1 the iron hypothesis posits a role for increased supply of mineral aerosol to the ocean surface during glacial periods in driving atmospheric co2 lower that changes in co2 and climate strongly affect dust supply raises the possibility of feedback here i take a systems view in analyzing the properties and implications of such a feedback and consider three primary state variables that can be related empirically to each other dust supply atmospheric co2 and climate surface air temperature the results of this analysis suggest that the dust co2 climate feedback is primarily an intraglacial phenomenon when it can account for about a third of the temperature variability recorded in antarctic ice cores since glacial interglacial cyclicity prior to ca 800 kyr bp is characterized by the absence of a full glacial state such as the last glacial maximum it is possible that destabilization of climate by the marine iron cycle is fundamental to the differences between 41 kyr and 100 kyr climatic regimes the critical role played by the state of the land surface in this feedback also has implications for the longer term evolution of the earth system during the cenozoic

feedback between aeolian dust climate and atmospheric co2 in glacial time 1 enhanced aeolian supply of iron to the biota of the southern ocean during glacial periods is suspected to be an important contributory mechanism to the concurrently low observed mixing ratios of atmospheric co2 declining rates of dust deposition prior to the glacial terminations may be critical in driving the initial deglacial rise in co2 but the reasons behind the dust decline itself are as yet unknown here we show that the dust record from the vostok ice core can be qualitatively derived from a few general assumptions regarding the formation and aging of patagonian sources of aeolian material and the efficiency with which it is transported through the atmosphere we suggest that during glacial periods this dust supply becomes particularly sensitive to changes in global climate and that in turn climate is responsive to the dust due to iron fertilization this positive feedback may mean that during glacial periods the carbon cycle exhibits two quasi steady states characterized by distinct co2 concentrations recognition of this glacial subcycle may help to account for the timing and sequence of events at the terminations

carbon isotopic records of middle holocene corals and environmental causes in northern south china sea two high resolution delta c 13 records of similar to 5 4 and similar to 4 4 ka coral colonies porites lutea from east coast of hainan island in the northern south china sea scs provide insights into the complex links between coral carbon isotopes and environment changes the delta c 13 of the similar to 5 4 ka coral offered a 40 year growth history with an average of 2 62 parts per thousand and amplitude of 2 96 parts per thousand the similar to 4 4 ka coral s revealed a 55 year growth history with an average of 3 12 parts per thousand and amplitude of 4 21 parts per thousand which revealed higher coral delta c 13 and increased seasonality in the middle holocene our analysis suggests that the higher coral delta c 13 was the combined result of higher radiation salinity and nutrient level and lower atmosphere co2 concentration which might increase coral delta c 13 through strengthening photosynthesis of symbiont zooxanthella in the context of kinetic and metabolic fractionations the increased seasonality was mostly produced by strengthened radiation the decreasing standard deviation of the similar to 5 4 ka coral annual delta c 13 revealed weakened interannual changes of atmospheric co2 salinity and nutrient by contrast the increasing deviation of the similar to 4 4 ka coral delta c 13 suggests strengthened interannual changes of these variables the similar to 5 4 ka coral delta c 13 showed a long term increasing trend at a rate of 0 33 increase y 1 which was attributed to natural decrease in atmospheric co2 and increasing salinity and nutrient level however the similar to 4 4 ka coral delta c 13 showed a long term decreasing trend at a rate of 0 25 decrease y 1 which was ascribed to unusual increase in atmospheric co2 and decreasing salinity and nutrient level c 2014 elsevier ltd and inqua all rights reserved

the potential role of peatland dynamics in ice age initiation abstract physical and chemical coupling of peatland vegetation soils and landforms and atmosphere creates feedbacks which may be important in ice age initiation a box diffusion co 2 exchange model shows that a transient forcing of 500 gt c the amount proposed to have accumulated in peatlands during the last interglacial glacial transition over 5000 yr results in a lowering of atmospheric co 2 by about 40 ppm proxy data indicate that a decrease in atmospheric co 2 may have occurred over the last 5000 yr up to preindustrial times and the amount is similar to that calculated from holocene peatland expansion 22 ppm these results suggest that models should consider the role of peatlands in ice age initiation

modeling the dynamics of terrestrial carbon storage since the last glacial maximum a dynamic global vegetation model dgvm was used to simulate global terrestrial carbon storage and stable carbon isotope composition changes for the last 21000 years a paleoclimate scenario was provided by interpolation of coupled agcm mixed layer ocean model experiments co2 atm data were obtained from the byrd and taylor dome ice core records according to the model results terrestrial carbon storage at the last glacial maximum lgm 21 ka was 821 pg c less than today the modeled isotopic composition delta 13 c of total terrestrial carbon at lgm was enriched by 1 5parts per thousand compared to present during the deglaciation 17 9 ka vegetation expanded rapidly into formerly glaciated areas and carbon storage correspondingly increased increasing npp sustained a continuing increase in terrestrial carbon storage through the holocene these results do not support the published hypothesis that terrestrial co2 outgassing drove the ca 20 ppm increase in co2 atm after 8 ka they are consistent with an alternative explanation based on the oceanic caco3 compensation response to the extraction of carbon from the atmosphere ocean system during the deglaciation

changes in ph in the eastern equatorial pacific across stage 5 6 boundary based on boron isotopes in foraminifera estimates of paleo ph for the eastern equatorial pacific ocean across the oxygen isotopic stage 5 6 boundary have been made based on the boron isotopic composition of planktonic orbulina universa and benthic mixed species foraminifera from core v19 28 the estimated deep ocean ph during the penultimate glacial period was about 0 3 0 1 ph units higher compared to the modern deep ocean this is consistent with previously estimated deep ocean ph changes across the stage l 2 boundary in the western equatorial pacific and tropical atlantic thus arguing against the possibility that the benthic foraminifera analyzed to estimate deep ocean ph changes have been significantly affected by anomalous local environment and or diagenesis the estimated changes in the deep ocean carbonate chemistry require a decoupling of several kilometers between the saturation horizon and the lysocline during the glacial periods though such a decoupling could be achieved by enhanced respiration co2 driven calcite dissolution in sediments during glacial periods it lacks support from the calcite sedimentary records the boron isotopic compositions of planktonic foraminifera on the other hand indicate no significant ph change in the eastern equatorial pacific surface ocean during the glacial interglacial transition this is inconsistent with an expected higher surface ocean ph during the glacial period due to lower atmospheric pco2 and is also in contrast with the previously estimated boron isotope based glacial interglacial ph change of 0 2 0 1 ph units in the western equatorial pacific and tropical atlantic the lack of change in eastern equatorial pacific surface ocean ph between glacial interglacial periods could be attributed to less nutrient utilization efficiency and or enhanced calcite production during glacial periods such a decrease in nutrient utilization efficiency and or increase in calcite production would lead to a greater disequilibrium between the pco2 of eastern equatorial pacific surface ocean and that of the atmosphere making this part of the ocean a greater source of co2 to the atmosphere during glacial periods compared to today

plate tectonic trigger of changes in pco2 and climate in the oxfordian late jurassic carbon isotope and modeling evidence abstract the transition from the middle to the late jurassic was characterized by significant changes in oceanography and climate and by changes in global carbon cycle as shown in the c isotope record a prominent mid oxfordian positive excursion in bulk carbonate carbon isotope values 13 c carb with an amplitude of more than 1 has been documented from many sections in the northern tethys realm in this study we present new bulk organic matter c isotope data 13 c org from northwestern tethys that do not record the mid oxfordian positive excursion in carbonate carbon on the contrary 13 c org decreases during the interval of the most rapid increase in 13 c carb we demonstrate that this decrease is not due to a changing marine terrestrial organic carbon partitioning but that the contrasting isotope trends record peculiar environmental and climate changes which occurred near the beginning of the late jurassic using a simple carbon cycle model we show that an increase in atmospheric p co 2 starting at modern levels could be the cause of contrasting trends in 13 c carb and 13 c org we suggest that a reorganisation of ocean currents related to the opening and or widening of the tethys atlantic pacific seaway and a massive spread of shallow sea carbonate production led to higher p co 2 model simulations indicate that this increase in p co 2 may have triggered changes in the biological carbon pump and in organic carbon burial that can explain the middle oxfordian c isotope record

is the magnitude of the carbonate ion decrease in the abyssal ocean over the last 8 kyr consistent with the 20 ppm rise in atmospheric co2 content 1 changes in the extent of shell fragmentation the wall thicknesses of foraminifera shells and the bulk caco3 content of deep pacific sediments demonstrate that the extent of dissolution has steadily increased during the past 8 kyr on the basis of measurements on sediment core top material from a range of water depths on the ontong java plateau these dissolution proxies have been calibrated allowing the extent of the decrease in carbonate ion concentration to be quantified the results suggest that the decrease was larger than that of 6 mol km expected to accompany the 20 atm rise in atmospheric co2 content that occurred during this time interval however the inconsistency between the magnitude of the change based on the decrease in shell weight on one hand and that based on the increase in fragmentation on the other hand is problematic if indeed the drop in carbonate ion concentration has been larger than expected then 8 kyr ago either a change in the pattern of thermohaline circulation or in the strength of the biological pump must have kicked in and become ever stronger as the millennia passed if thermohaline circulation is the villain then a possible explanation is that the strength of deepwater formation in the northern atlantic has weakened relative to that in the southern ocean

a new mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of poc with ballast minerals abstract in simulation studies of the ocean s role in the global carbon cycle predicting the depth distribution for remineralization of particulate organic carbon poc is of particular importance following sarmiento et al global biogeochemical cycles 7 1993 417 most simulation models have the power law curve of martin et al deep sea research 34 1987 267 for this purpose the martin et al curve is an empirical fit to data most of which is from shallow floating sediment traps using such a fit implies that all the information necessary for prediction is contained in the carbon flux itself so that the organic carbon flux f oc z at any depth z can be predicted from the flux of organic carbon f oc z 0 at some near surface depth z 0 here we challenge this basic premise arguing that fluxes of ballast minerals silicate and carbonate biominerals and dust determine deep water poc fluxes so that a mechanism based model of poc flux must simultaneously predict fluxes of both poc and ballast minerals this assertion is based on the empirical observation that poc fluxes are tightly linked quantitatively to fluxes of ballast minerals in the deep ocean here we develop a model structure that incorporates this observation and fit this model to us jgofs eqpac data this model structure plus the preliminary parameter estimates we have obtained can be used to explore the implications of our model in studies of the ocean carbon cycle

glacial interglacial rain ratio changes implications for atmospheric co2 and ocean sediment interaction abstract a reduction of the carbonate carbon to organic carbon export rain ratio during glacial times has been advanced to explain the glacial interglacial atmospheric co 2 variations this hypothesis is tested and implications for the dynamics of sedimentary carbonate preservation and dissolution are explored with a multi box model mbm of the ocean carbon cycle fully coupled to a new transient early diagenesis model called medusa a peak reduction of the rain ratio by 40 at the last glacial maximum lgm was found to produce a net atmospheric p co 2 reduction of about 40 ppm changing shelf carbonate accumulation rates and continental weathering inputs produced a 55 60 ppm reduction the combination of the two mechanisms generates a p co 2 change of 90 95 ppm which compares well with the observed data however the resulting model sedimentary record does not conform to actual sedimentary records the changes related to continental shelf processes and variable weathering flux depress the calcite saturation horizon csh by about 1 km at the lgm if rain ratio variations are also considered that depression increases by another km in addition to this large amplitude for the csh possibly due to the adopted box model approach the changing rain ratio also leads to transition zone changes in the model sedimentary record that are opposite in phase with data based reconstructions realistic changes in the aragonite fraction of the carbonate rain were found to have only a minimal impact on atmospheric p co 2 finally chemical erosion of deep sea sediment was shown to reduce the amplitude of variation of the sedimentary ccd by about 10 20 it may provide a mechanism to improve the model data agreement

deglacial climate carbon cycle and ocean chemistry changes in response to a terrestrial carbon release researchers have proposed that a significant portion of the post glacial rise in atmospheric co2 could be due to the respiration of permafrost carbon stocks that formed over the course of glaciation in this paper we used the university of victoria earth system climate model v 2 9 to simulate the deglacial and interglacial carbon cycle from the last glacial maximum to the present the model s sensitivity to mid and high latitude terrestrial carbon storage is evaluated by including a 600 pg c carbon pool parameterized to respire in concert with decreases in ice sheet surface area the respiration of this stored carbon during the early stages of deglaciation had a large effect on the carbon cycle in these simulations allowing atmospheric co2 to increase by 40 ppmv in the model with an additional 20 ppmv increase occurring in the case of a more realistic prescribed co2 radiative warming these increases occurred prior to large scale carbon uptake due to the reestablishment of boreal forests and peatlands in the proxy record beginning in the early holocene surprisingly the large external carbon input to the atmosphere and oceans did not increase sediment dissolution and mean ocean alkalinity relative to a control simulation without the high latitude carbon reservoir in addition our simulations suggest that an early deglacial terrestrial carbon release may come closer to explaining some observed deglacial changes in deep ocean carbonate concentrations than simulations without such a release we conclude that the respiration of glacial soil carbon stores may have been an important contributor to the deglacial co2 rise particularly in the early stages of deglaciation

isotopic responses to basaltic injections into silicic magma chambers a whole rock and microsampling study of macrorhythmic units in the pleasant bay layered gabbro diorite complex maine usa the pleasant bay layered gabbro diorite complex 420 ma formed via repeated injections of mafic magma into a felsic magma chamber it is dominated by repeating sequences macrorhythmic units with chilled gabbroic bases which may grade upward into medium grained gabbro diorite and granite each unit represents an injection of mafic magma into the chamber followed by differentiation increases in sri and decreases in endi with stratigraphic height indicate open system isotopic behaviour and exchange between the mafic and felsic magmas isotopic variations of whole rock samples in individual macrorhythmic units do not conform to bulk mixing or afc models between potential parental magmas sr isotopic studies of single feldspar crystals from one macrorhythmic unit indicate that exchange of crystals between the resident felsic magma and mafic influxes was important that some of the rocks contain feldspar xenocrysts and that the rocks are isotopically heterogeneous on an intercrystal scale xenocryst abundance increases with stratigraphic height suggesting that crystal exchange occurred in situ the lack of disequilibrium textures in the xenocrystic feldspar indicates the evolved macrorhythmic magma and resident silicic magma were of a similar composition and likely in thermal equilibrium at the time of crystal transfer mafic chilled margins are enriched in alkalis and isotopically evolved compared with mafic dikes representing the parental melts and suggest rapid in situ diffusional exchange following emplacement of individual mafic replenishments

holocene climate and carbon cycle dynamics experiments with the green mcgill paleoclimate model 1 an inverse method is used to investigate the global carbon cycle from the early holocene 8 kyr bp to the end of the pre industrial period 0 kyr bp in an improved version of the green mcgill paleoclimate model mpm in this paper we now take into account the vegetation precipitation feedback and evaluate the terrestrial carbon cycle for the pre industrial equilibrium from our coupled transient simulation under orbital forcing reconstructed taylor dome atmospheric co2 forcing and a prescribed retreating laurentide ice sheet lis we find a decrease of 70 pgc in total carbon storage in the sahara region 15 degrees n to 30 degrees n and 15 degrees w to 50 degrees e which is caused by the desertification simulated in the green mpm the above decrease is partially compensated by an increase of 40 pgc in total carbon storage in the southern hemisphere from 8 to 2 kyr bp from an analysis of the total carbon stored under the ice sheet we can infer that this carbon has negligible impact on atmospheric co2 after 8 kyr bp from our model results we further conclude that the retreating lis together with the vegetation albedo feedback cause the global terrestrial carbon to increase from 8 to 6 kyr bp the application of the inverse method suggests that the first 10 ppmv increase in atmospheric co2 from 8 to 6 kyr bp comes from the ocean finally in the model simulations the total terrestrial carbon release from 6 to 0 kyr bp is about 68 to 95 pgc which would produce about a 5 to 7 ppmv atmospheric co2 increase based on the calculation of joos et al 2004 owing to our model limitation there is no ocean carbon cycle we cannot conclude whether the overall oceanic co2 release from 8 to 0 kyr bp is due to outgassing related to sst changes or to calcite compensation as proposed by broecker et al 2001

deep south atlantic carbonate chemistry and increased interocean deep water exchange during last deglaciation abstract carbon release from the deep ocean at glacial terminations is a critical component of past climate change but the underlying mechanisms remain poorly understood we present a 28 000 year high resolution record of carbonate ion concentration a key parameter of the global carbon cycle at 5 km water depth in the south atlantic we observe similar carbonate ion concentrations between the last glacial maximum and the late holocene despite elevated concentrations in the glacial surface ocean this strongly supports the importance of respiratory carbon accumulation in a stratified deep ocean for atmospheric co 2 reduction during the last ice age after 9 mol kg decline during heinrich stadial 1 deep south atlantic carbonate ion concentration rose by 24 mol kg from the onset of bolling to pre boreal likely caused by strengthening north atlantic deep water formation bolling or increased ventilation in the southern ocean younger drays or both pre boreal the 15 mol kg decline in deep water carbonate ion since 10 ka is consistent with extraction of alkalinity from seawater by deep sea caco 3 compensation and coral reef growth on continental shelves during the holocene between 16 600 and 15 000 years ago deep south atlantic carbonate ion values converged with those at 3 4 km water depth in the western equatorial pacific as did carbon isotope and radiocarbon values these observations suggest a period of enhanced lateral exchange of carbon between the deep south atlantic and pacific oceans probably due to an increased transfer of momentum from southern westerlies to the southern ocean by spreading carbon rich deep pacific waters around antarctica for upwelling invigorated interocean deep water exchange would lead to more efficient co 2 degassing from the southern ocean and thus to an atmospheric co 2 rise during the early deglaciation

modeled estimates of global reef habitat and carbonate production since the last glacial maximum estimated changes in reef area and caco3 production since the last glacial maximum lgm are presented for the first time based on a model reefhab which uses measured environmental data to predict global distribution of reef habitat suitable reef habitat is defined by temperature salinity nutrients and the depth attenuated level of photosynthetically available radiation par caco3 production is calculated as a function of par when minimum par levels were chosen to restrict reef growth to 30 m depth and less modern reef area totaled 584 746 10 km global carbonate production which takes into account topographic relief as a control on carbonate accumulation was 1 00 gt yr 1 these values are close to the most widely accepted estimates of reef area and carbonate production and demonstrate that basic environmental data can be used to define reef habitat and calcification to simulate reef habitat changes since the lgm the model was run at 1 kyr intervals using appropriate sea level and temperature values these runs show that at the lgm reef area was restricted to 20 of that today and carbonate production to 27 due primarily to a reduction in available space at the lower sea level and secondarily to lower sea surface temperatures nonetheless these values suggest that reef growth prior to shelf flooding was more extensive than previously thought a crude estimate of reef released co2 to the atmosphere since the lgm is of the same order of magnitude as the atmospheric co2 change recorded in the vostok ice core which emphasizes the role of neritic carbonates within the global carbon cycle this model currently addresses only the major physical and chemical controls on reef carbonate production but it provides a template for estimating shallow tropical carbonate production both in the present and in the past as such the model highlights several long standing issues regarding reef carbonates particularly in terms of better defining the roles of light temperature aragonite saturation state and topography on reef calcification

sphagnum peatland distribution in north america and eurasia during the past 21 000 years the distribution and abundance of sphagnum spores in north america and eurasia are mapped for the past 21 ka the present day distribution of abundant sphagnum spores corresponds closely to areas with peatland development with maximum sphagnum abundance between 630 and 1300 mm annual precipitation and between 2 and 6 c mean annual air temperature during the wisconsin glaciation there were apparently not large areas of peatland in north america except in alaska high sphagnum spore percentages were found in eastern north america during deglaciation major peatland development occurred in boreal north america after 9 ka and there was a southward movement of high sphagnum spore abundance after 5 ka in the western great lakes region major peatland development began after 9 ka in europe and asia on the basis of maps of the area supporting peatlands carbon accumulation in peatlands is estimated to be low prior to 11 ka increased slightly between 11 and 5 ka and greatly increased during the past 5 ka

impact of the ocean carbonate chemistry on living foraminiferal shell weight comment on carbonate ion concentration in glacial age deep waters of the caribbean sea by w s broecker and e clark broecker and clark 2002 use the size normalized weight of planktic foraminifera to estimate the carbonate ion concentration co3 of atlantic glacial upper deep water this method was introduced by lohmann 1995 and is based on the fact that within a defined size fraction dissolution decreases shell weight in proportion to the degree of undersaturation with respect to caco3 based on the following assumptions 1 the thickness of the foraminiferal shell wall does not depend on growth conditions 2 the saturation co3 for calcite co3 sat increases by 20 mol kg 1 km 1 broecker and clark 2001 3 the weight loss slope is universal and ca 0 3 g mol kg 1 1 broecker and clark 2001 4 the offset between the bottom water and pore water co3 was the same during glacial time as during the holocene broecker and clark 2002 calculate that the co3 of atlantic glacial upper deep water was 14 mol kg 1 higher than during the holocene although they recognize that some of their assumptions are not strictly valid they do not assess the impact of those assumptions on their co3 estimate here we comment on several of those assumptions and attempt to quantify their impact on broecker and clark s 2002 calculations

observational constraints on the causes of holocene co2 change the mechanisms that controlled past atmospheric co2 levels are not directly measurable hence many proxy data sources are combined when reconstructing past carbon cycling the accuracy of holocene modeling reconstructions is checked by seeking consistency between data based observables and their numerically simulated counterparts a new framework is presented to evaluate which combinations of observables can best constrain carbon cycle mechanisms with the minimum of uncertainty we show that when previous studies have combined ocean temperatures ocean co32 and the 13c of atmospheric co2 as observables uncertainties in the data sources are amplified by over 2 orders of magnitude when reconstructing the mechanisms responsible for co2 increase however incorporating mean 13c of ocean dic since 8000 years ago as an additional data source reduces the uncertainties by more than a factor of 5 making this observable a priority for future research our analysis indicates that the 20 ppm increase in co2 between 8000 years bp and preindustrial was caused by significant caco3 precipitation and a reduction in the ocean soft tissue pump meanwhile an increase in terrestrial carbon storage opposed the co2 increase the methods presented here are useful for investigating a range of paleoclimate events

a model based interpretation of low frequency changes in the carbon cycle during the last 120 000 years and its implications for the reconstruction of atmospheric δ14c a main caveat in the interpretation of observed changes in atmospheric d14c during the last 50 000 years is the unknown variability of the carbon cycle which together with changes in the 14c production rates determines the 14c dynamics a plausible scenario explaining glacial interglacial dynamics seen in atmospheric co2 and d13c was proposed recent ly kohler et al 2005 a similar approach and expanding its interpretation to the 14c cycle is an important step towards a deeper understanding of d14c variability this approach is based on an ocean atmosphere biosphere box model of the global carbon cycle bicycle to reproduce low freque ncy changes in atmospheric co2 as seen in antarctic ice cores the model is forced forward in time by various paleo climatic records derived from ice and sediment cores the simulation results of our proposed scenario match a compiled co2 record from various ice cores during the last 120 000 years with high accuracy r2 0 89 we analyze scenarios with different 14c production rates which are either constant based on 10be measured in greenland ice cores or the recent high resolution geomagnetic field reconstruction glopis 75 and compare them with the available d14c data covering the last 50 000 years our results suggest that during the last glacial cycle in general less than 110 o oo of the increased atmospheric d14c are based on variations in the carbon cycle while the largest part 5 6 of the variations has to be explained by other factors glacial atmospheric d14c larger than 700 o oo cannot not be explained within our framework neither through carbon cycle based changes nor through variable 14c production superimposed on these general trends might lie positive anomalies in atmospheric d14c of 50 o oo caused by millennial scale variability of the northern deep water production during heinrich events and dansgaard oeschger climate fluctuations according to our model the dominant processes that increase glacial d14c are a reduced glacial ocean circulation 40 o oo a restricted glacial gas exchange between the atmosphere and the surface ocean through sea ice coverage 20 o oo and the enrichment of dic with 14c in the surface waters through isotopic fractionation during higher glacial marine export production caused by iron fertilization 10 o oo

evidence for a reduction in the carbonate ion content of the deep sea during the course of the holocene the paleo carbonate ion proxy proposed by broecker et al 1999 is applied in a search for trends in the holocene acidity of waters in the transition zone between north atlantic deep water and antarctic bottom water aabw a clear signal emerges that the carbonate ion content of waters in this zone declined during the past 8000 years in order to determine whether this decline represents a strengthening of the northward penetrating tongue of low co3 content aabw or a global reduction of co3 ion measurements were made on a core from the ontong java plateau in the western equatorial pacific evidence for a similar decline in co3 ion over the course of the holocene was obtained lending support of the latter explanation such a drop is consistent with the recent finding by indermuhle et al 1999 that the co2 content of the atmosphere as recorded in the taylor dome antarctica ice core rose by 20 25 ppm during the past 8000 years

high resolution quantitative imaging of plagioclase composition using accumulated backscattered electron images new constraints on oscillatory zoning oscillatory zoning in plagioclase is investigated at small scale 10 m using accumulated backscattered electron bse images as high resolution imaging method combined with electron microprobe quantitative analysis gray value profiles across these images can be calibrated for an content with a resolution of 0 5 mol an applied to oscillatory zoned crystals this new application of bse imaging allows better characterization of zoning patterns along a profile and quantification of wavelength amplitude and shape of the oscillations we also obtain high resolution information on the morphology of growth zones boundaries this approach allows us to better classify the different types of oscillations and concentric zoning dissolution is more frequent than usually recognized major resorption surfaces crosscut several growth zones irregular 5 10 m saw tooth zones are delimited by faint wavy dissolution surfaces and must be distinguished from small scale oscillations 1 3 m with straight boundaries this suggests at least two mechanisms for the formation of these zoning patterns faint oscillations are probably caused by local kinetic control whereas wavy dissolution surfaces involve magma chamber dynamics

association of sinking organic matter with various types of mineral ballast in the deep sea implications for the rain ratio 1 we compiled and standardized sediment trap data below 1000 m depth from 52 locations around the globe to infer the implications of the armstrong et al 2002 ballast model to the ratio of organic carbon to calcium carbonate in the deep sea the rain ratio we distinguished three forms of mineral ballast calcium carbonate opal and lithogenic material we concur with armstrong et al 2002 that organic carbon sinking fluxes correlate tightly with mineral fluxes based on the correlations seen in the trap data we conclude that most of the organic carbon rain in the deep sea is carried by calcium carbonate because it is denser than opal and more abundant than terrigenous material this analysis explains the constancy of the organic carbon to calcium carbonate rain ratio in the deep sea today and argues against large changes in the mean value of this ratio in the past however sediment trap data show variability in the ratio in areas of high relative calcium carbonate export mass caco3 mass ratio 0 4 unexplainable by the model leaving open the possibility of regional variations in the rain ratio in the past

a new 27 ky high resolution east antarctic climate record the ice core recently drilled at the dome concordia site on the east antarctic plateau provides a new high resolution isotope record covering part of the last glacial the last transition and the holocene the two step shape of the deglaciation is remarkably similar for all the ice cores now available on the east antarctic plateau the first warming trend ends about 14000 years ago and is followed by the well marked antarctic cold reversal acr with a secondary peak common to all records during the deglaciation there are more similarities between the near coastal site of taylor dome and inland east antarctica than between taylor dome and central greenland however the results for epica do appear to confirm the taylor dome timescale after about 14 ka showing cooling into the acr roughly in phase between greenland and antarctica while the overall deglacial pattern is asynchronous this suggests that the now classical picture of a temperature seesaw between antarctica and greenland may be too simplistic

influence of variable rates of neritic carbonate deposition on atmospheric carbon dioxide and pelagic sediments short term imbalances in the global cycle of shallow water calcium carbonate deposition and dissolution may be responsible for much of the observed pleistocene change in atmospheric carbon dioxide content however any proposed changes in the alkalinity balance of the ocean must be reconciled with the sedimentary record of deep sea carbonates the possible magnitude of the effect of shallow water carbonate deposition on the dissolution of pelagic carbonate can be tested using numerical simulations of the global carbon cycle boundary conditions can be defined by using extant shallow water carbonate accumulation data and pelagic carbonate deposition dissolution data on timescales of thousands of years carbonate deposition versus dissolution is rarely out of equilibrium by more than 1 5 x 10 13 mole yr 1 results indicate that the carbonate chemistry of the ocean is rarely at equilibrium on timescales less than 10 ka this disequilibrium is probably due to sea level induced changes in shallow water calcium carbonate deposition dissolution an interpretation that does not conflict with pelagic sedimentary data from the central pacific

what caused the atmosphere s co2 content to rise during the last 8000 years 1 we make a case that the 20 ppm rise in atmospheric co2 content over the last 8000 years was at least in part a consequence of the 500 gt c increase in terrestrial biomass early in the present interglacial rather than of a 200 gt c decrease in terrestrial biomass during the latter part of the holocene as proposed by indermuhle et al 1999 in support of this claim we present new 13c measurements from an ontong java plateau box core which do not reproduce the trend deduced from measurements on co2 from the taylor dome ice core in attempt to distinguish between scenarios put forth to accounting for the late holocene rise in atmospheric co2 content we also made foraminifera shell weight measurements on three box cores from the ontong java plateau we were surprised to find that the early holocene caco3 preservation event we sought was strongly depth dependent the largest magnitude was at 4 km where co3 ion concentrations appear to have been 30 mol kg higher than today s and hence nearly as high as those in today s north atlantic deep water

deep sea carbonate preservation in the western philippine sea over the past 1ma abstract in this paper we present a continuous record of calcium carbonate caco 3 content that covers the last 1 ma from core md06 3050 15 57 0943 n 124 46 7747 e water depth 2967 m which was collected in the western philippine sea wps the caco 3 content in this study core is characterized by maxima during deglaciations and minima during the onsets of glacial periods and generally shows pacific style patterns with relatively high and low values during glacial and interglacial periods respectively proxies of dissolution and primary productivity pp the caco 3 content and the oxygen isotope record from this core are compared throughout the 1 ma study interval to improve our understanding of the mechanisms that affected carbonate preservation and dissolution at this site the planktonic foraminifera shell fragmentation ratio shell fragment is used as a dissolution proxy in this study the shell fragment data from md06 3050 provide evidence of preservation maxima during most of the deglaciations whereas intense dissolution is recorded at the onsets of glacial periods within the past 1 ma the variations in shell fragments are similar to those seen in the caco 3 content which demonstrates that the bulk caco 3 content patterns were controlled by dissolution in deep seawater the primary productivity from the coccolith record shows limited similarity with the caco 3 content on glacial interglacial time scales since 1 ma which suggests that pp played a negligible role in the glacial interglacial caco 3 cycle however a bloom of the coccolithophores geophyrocapsa caribbeanica that extended from mis 9 to mis 12 likely contributed to the increased caco 3 content observed during the mid brunhes interval mbe over the glacial interglacial fluctuations therefore the caco 3 content should be used as a dissolution proxy with caution during the mbe in the tropical pacific especially for water depths that are shallower than the carbonate lysocline

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

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

holocene atmospheric co2 increase as viewed from the seafloor 1 three scenarios have been proposed to explain the 20 ppm post 8000 bp rise in atmospheric co2 content indermuhle et al 1999 call on a climate induced decrease in terrestrial biomass w f ruddiman personal communication 2002 calls on an anthropogenically induced decrease in terrestrial biomass broecker et al 2001 suggest instead that this rise in co2 was a response to a caco3 preservation event induced by an early holocene increase in terrestrial biomass the biomass decline hypothesis not only rests on shaky 13c data but also requires an unreasonably large decrease in biomass 195 40 gtc while evidence for a decrease in deep sea carbonate ion concentration over the last 8000 years reconstructed from caco3 size index and foraminifera shell weight measurements appears to support the idea that the co2 rise was caused by a change in the inventory of terrestrial biomass the decrease appears to be too large to be explained solely in this way regardless the co3 decline cannot be used to distinguish between the late holocene biomass decrease and early holocene biomass increase scenarios only when a convincing 13c record for atmospheric co2 has been generated will it be possible to make this distinction

coupled caal nasi diffusion in plagioclase feldspar experiments and applications to cooling rate speedometry abstract the rate of caal nasi interdiffusion in plagioclase feldspar was determined under 1 atm anhydrous conditions over the temperature range 1400 to 1000 c in calcic plagioclase an80 81 by homogenizing coherent exsolution lamellae the dependence of the average interdiffusion coefficient on temperature is given by the expression d 10 99 cm 2 sec exp 123 4 kcal mol rt t in k this value is for diffusion perpendicular to the 03 1 interface of the lamellae caal nasi interdiffusion is 4 to 5 orders of magnitude slower than oxygen diffusion in the temperature range 1400 to 1200 c and possibly 10 orders of magnitude slower at subsolidus temperatures the large differences in diffusion rates explain the apparent contradiction posed by the plagioclases of large layered intrusions e g the skaergaard which retain delicate ca na compositional zoning profiles on the micron scale but have undergone complete oxygen isotopic exchange with heated meteoric groundwater from the surrounding wall rocks caal nasi diffusion is slow the closure temperature is high within the solidus liquidus interval and ca na zoning is preserved oxygen diffusion is faster the closure temperature is lower 350 400 c and the feldspars exchange oxygen with the low temperature hydrothermal fluids the complex micron scale oscillatory zones in plagioclase can also be used as cooling rate speedometers for volcanic and plutonic plagioclase cooling histories typical of large mafic intrusions e g the stillwater are slow begin at high initial temperatures 1200 c and result in homogenization of oscillatory zones on the scale of 10 microns the oscillatory zones found in the plagioclase of granodioritic plutons are preserved because cooling is initiated at a lower temperature 1000 c limiting diffusion to submicron length scales despite the slow cooling rate of the intrusion

an end to the rain ratio reign 1 one of the most elegant mechanisms forwarded for late quaternary atmospheric co2 variability concerns the sensitivity of calcium carbonate preservation in deep ocean sediments to the relative delivery rates of calcium carbonate and particulate organic carbon the caco3 poc rain ratio it was implicitly assumed that any change in the caco3 poc rain ratio of biogenic material produced in the surface ocean will be communicated directly to the sediments this would allow relatively subtle shifts in ecosystem composition to affect sedimentary caco3 preservation and thus atmospheric co2 however recent research into the controls on the transport of poc to depth suggests that the rain ratio seen by the sediments may instead be buffered against any perturbation occurring at the surface this casts doubt on the viability of hypotheses envisaging ecological changes as a means of accounting for the observed glacial interglacial co2 signal

holocene sediments of wistari reef towards a global quantification of coral reef related neritic sedimentation in the holocene wistari reef within the southern great barrier reef is a shallow coral reef platform featuring a very clearly defined leeward accretionary wedge of carbonate sediments the total global area of shallowly submerged coral reef has been quantified as 255 000 km 2 the question then becomes what additional area of sediment of significant thickness is associated with the measured shallow reef areas t at wistari reef the leeward sedimentary wedge has an area and a thickness that are roughly equal to the holocene sediments that have accumulated on the platform several important observations can be made from these data firstly the area of significant neritic carbonate sedimentation 1 m ka associated with coral reefs is near 500000 km 2 secondly the production rate of neritic carbonates at wistari reef is almost 50 less than the accumulation rate needed to obtain the volume of holocene reef sediments observed this implies that both production and accumulation neritic carbonate must have been more than a factor of two higher in the early to mid holocene c 2001 elsevier science b v all rights reserved

linkages between rapid climate variability and deep sea benthic foraminifera in the deep subantarctic south atlantic during the last 95 kyr we present a high resolution record of benthic foraminifera fauna from a sediment core retrieved from the south cape basin subantarctic south atlantic spanning the last glacial cycle 95 kyr information provided by benthic foraminiferal assemblages together with paleoclimate proxies from the same core allow us to interpret changes in the style of primary production episodic versus sustained in relation to abrupt climate oscillations our results indicate that fluctuations in the abundance of the phytodetritus related species epistominella exigua are concomitant with millennial scale high latitude climate perturbations episodic phytoplankton blooms increased during a negative mode of the bipolar seesaw irrespective of the magnitude of the perturbation i e heinrich stadial versus non heinrich stadial events we provide a hypothesis linking the frequency and intensity of these events to atmospheric perturbations interhemispheric climate variability and millennial scale changes in atmospheric co2 a notable exception to the overall pattern is the generally high abundance of e exigua across the globally synchronous onset of glacial marine oxygen isotope stage mis 4 a period generally characterized by increased dustiness and low quality organic carbon as inferred by the percentage of the nonphytodetritus species this highlights the special characteristics governing the onset of mis 4 in the subantarctic

towards the time dependent modeling of sediment core data on a global basis the procedure for the simulation of a time dependent sediment stratigraphy for 4 different sediment species with a global biogeochemical ocean general circulation model is presented in this feasibility study a sediment column for the last 131 kyr was accumulated through use of a variable ocean velocity field mixed from preindustrial and glacial ocean time slices in a kinematic approach the biogenic components of sediment are entirely a model product artificial sediment cores were recovered from the simulated stratigraphy the approach is the foundation for a systematic comparison of paleoclimate simulations with the sediment record through use of adjoint model codes the direct 4 dimensional data assimilation of paleoclimate observations will become possible in the long range

transient simulations of holocene atmospheric carbon dioxide and terrestrial carbon since the last glacial maximum 1 conflicting hypotheses are investigated for the observed atmospheric co2 increase of 20 ppm between 8 ka bp and pre industrial time the carbon component of the bern carbon cycle climate bern cc model which couples the lund potsdam jena dynamic global vegetation model to an atmosphere ocean sediment component is driven by climate fields from time slice simulations of the past 21 ka with the hadley centre unified model or the ncar climate system model the entire holocene ice core record of co2 is matched within a few ppm for the standard model setup and results are broadly consistent with proxy data of atmospheric 13 co2 mean ocean d 13 c and pollen data within their uncertainties our analysis suggests that a range of mechanisms including calcite compensation in response to earlier terrestrial uptake terrestrial carbon uptake and release sst changes and coral reef buildup contributed to the 20 ppm rise the deep sea d 13 c record constrains the contribution of the calcite compensation mechanism to 4 10 ppm terrestrial carbon inventory changes related to climate and co2 forcing the greening of the sahara peat buildup and land use have probably influenced atmospheric co2 by a few ppm only the early holocene co2 decrease is quantitatively explained by terrestrial uptake and calcite compensation in response to terrestrial uptake during the glacial interglacial transition the recent hypothesis by ruddiman 2003 that anthropogenic land use caused a 40 ppm co2 anomaly over the past 8 ka preventing the climate system from entering a new glacial would imply an anthropogenic emission of 700 gtc and a decrease in atmospheric d 13 co f 0 6 permil this is not compatible with the ice core d 13 c record and would require an upward revision of land use emission estimates by a factor of 3 to 4 index terms 0322 atmospheric composition and structure constituent sources and sinks 0315 atmospheric composition and structure biosphere atmosphere interactions 1615 global change biogeochemical processes 4805 1610 global change atmosphere 0315 0325 keywords carbon cycle modeling carbon dioxide holocene