boron isotopes and b ca in benthic foraminifera proxies for the deep ocean carbonate system abstract accurate records of the state of the ocean carbonate system are critical for understanding past changes in pco 2 ocean acidification and climate the chemical principles underlying the proxy of oceanic ph provided by the boron isotope ratio of foraminiferal carbonate are relatively well understood but the proxy s reliability has been questioned we present 76 new multi collector inductively coupled plasma mass spectrometry mc icpms 11 b measurements on a range of benthic foraminifera from 23 late holocene samples from the atlantic that reaffirm the utility of the 11 b ph proxy our boron isotope measurements on 10 benthic foraminifera tests typically yield a precision of 0 25 at 2 s d equivalent to 0 03 ph units 11 b values of epifaunal species are within analytical uncertainty of those predicted from a simple model assuming sole incorporation of b oh 4 from seawater and no vital effects using the independently determined fractionation factor of 1 0272 between 11 b 10 b of aqueous boron species infaunal foraminifera are consistent with this model but record the combined effects of lower pore water 11 b and ph no influence of partial dissolution or shell size on 11 b is observed we have also measured the b ca ratios of the same samples for individual cibicidoides species b ca shows a good correlation with co 3 2 but the b ca of different co occurring species morphotypes varies considerably these effects are not seen in 11 b which may therefore provide a more robust proxy of the ocean carbonate system whilst in theory 11 b and b ca can be combined to provide a quantitative reconstruction of alkalinity and dissolved inorganic carbonate dic in practice this is precluded by propagated uncertainties 11 b data give significant constraints on foraminifera calcification mechanisms and seem most simply explained by incorporation of b oh 4 into a hco 3 pool which is then completely incorporated in foraminiferal caco 3 our demonstration of the predictable variation of 11 b with ph across a wide range of species and locations provides confidence in the application of mc icpms measurements of foraminiferal 11 b to reconstruct past changes in the ocean carbonate system

discrete plio pleistocene phases of tilting and counterclockwise rotation in the southeastern aegean arc rhodos greece early pliocene formation of the south aegean left lateral strike slip system the island of rhodos represents an uplifted block in the largely submerged southeastern aegean forearc it has a complex history of subsidence uplift and counterclockwise rotation during the plio pleistocene in response to the interplay between large scale geodynamic processes in this paper we present a new chronostratigraphic framework for the continental pliocene apolakkia basin of southwestern rhodos we combine these time constraints with recently published chronostratigraphic data from the marine plio pleistocene basins of northeastern rhodos to reconstruct rotational and vertical motions our palaeomagnetic results identify two rotation phases for rhodos c 10 9 6 counterclockwise ccw rotation between 3 8 and 3 6 ma and c 17 6 ccw rotation since 0 8 ma between these phases rhodos tilted to the se drowning the southeastern coast to a depth of 500 600 m between 2 5 and 1 8 ma then to the nw which resulted in the re emergence of the drowned relief between 1 5 and 1 1 ma we relate the rotations of rhodos to incipient formation of the south aegean sinistral strike slip system and the foundering of the rhodos basin the previously shown absence of messinian evaporites in the deep marine rhodos basin in combination with the 3 8 ma onset of ccw rotation of rhodos constrains the onset of the formation of the south aegean strike slip system between 5 3 and 3 8 ma the formation of this strike slip system is probably related to the interplay of oblique collision between the southeastern aegean region and the northward moving african plate the westward motion of anatolia gravitational spreading of the overthickened aegean lithosphere and the recently postulated southwestward retreat of the african subducted slab along a subduction transform edge propagator fault

glacial carbonate dissolution cycles and atmospheric pco2 a view from the ocean bottom we present a calculation of the global calcium carbonate dissolution response to glacial interglacial changes in seawater carbonate chemistry inferred from cd ca and carbon isotope ratios in benthic foraminifera our model is based on the relationship between the carbonate dissolution flux and the degree of calcite saturation in the three main ocean basins the rate of carbonate dissolution is derived using mechanisms inferred from studies of surface sediment pore water geochemistry the model predicts a change in the relative importance of caco3 burial among the atlantic indian and pacific oceans between glacial and interglacial times chemical rearrangement of deep waters appears to be a viable mechanism for driving interocean differences in carbonate accumulation and observed caco3 burial trends constrain alkalinity changes that accompanied deepwater nutrient redistribution our model predicts atmospheric pco2 lowering during glacial times caused by the carbonate dissolution response to be less than 10 ppm suggesting that this mechanism is not a viable candidate for explaining a large fraction of the observed 80 ppm decrease observed in ice cores

the salinity temperature and δ18o of the glacial deep ocean we use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from ocean drilling program cores to reconstruct salinity and temperature of the deep ocean during the last glacial maximum lgm our data show that the temperatures of the deep pacific southern and atlantic oceans during the lgm were relatively homogeneous and within error of the freezing point of seawater at the ocean s surface our chloride data show that the glacial stratification was dominated by salinity variations in contrast with the modern ocean for which temperature plays a primary role during the lgm the southern ocean contained the saltiest water in the deep ocean this reversal of the modern salinity contrast between the north and south atlantic implies that the freshwater budget at the poles must have been quite different a strict conversion of mean salinity at the lgm to equivalent sea level change yields a value in excess of 140 meters however the storage of fresh water in ice shelves and or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

modern and pleistocene boron isotope composition of the benthic foraminifer cibicidoides wuellerstorfi abstract here we present the first species specific study of boron isotopes in the epibenthic foraminifer species cibicidoides wuellerstorfi coretop samples from a water depth profile from 1000 to 4500 m on the northern flank of the walvis ridge are 4 4 lower than the values expected based on calculations of the 11bborate of ambient seawater similar values for this foraminifer species are presented from odp site 668b at the sierra leone rise in the equatorial atlantic the consistency between data of the same species suggests the offsets are primary rather than diagenetic glacial c wuellerstorfi from odp 668b and walvis ridge have boron isotope compositions only slightly different to interglacial samples that is no larger than 0 10 ph units or 23 mol kg 1 in co32 above the reconstructed glacial lysocline and 0 07 ph units or 14 mol kg 1 in co32 below we use these results to suggest that glacial deep water ph in the atlantic was similar to interglacial ph the new data resolve the inconsistency between the previously reported high bottom water ph and the lack of significant carbonate preservation of the glacial deep ocean

global chemical erosion during the last glacial maximum and the present sensitivity to changes in lithology and hydrology geographically based calculations for 18 000 years ago 18 ka and today were made to examine the potential effects on terrestrial chemical erosion of changes in lithology and hydrology on glacial interglacial timescales runoff fields were derived from general circulation model predictions of precipitation minus evaporation then global lithologic maps were prepared so that empirical relationships for runoff versus bicarbonate flux for different rock types could be used to calculate global chemical erosion rates assuming that significant chemical erosion does not occur beneath ice sheets we find that chemical erosion in ice free areas at 18 ka was only slightly greater than today this result arises because the amount of land covered by ice sheets is roughly compensated for by exposed shelf areas and because there is little difference in global runoff the small 20 increase in the global chemical erosion rate during glacial conditions is due to exposure on the shelves of a relatively high proportion of carbonates which weather faster than average data on glacial interglacial movements of the calcite compensation depth ccd are inconclusive but seem to indicate little change whereas even a 20 increase in the riverine bicarbonate flux should cause an observable deepening if the ccd did not indeed change then our predicted increase in the bicarbonate flux from land during glaciations would have to be accommodated by other means such as increased carbonate productivity about half of the observed decrease in atmospheric pco2 at 18 ka could be explained if increased silicate chemical erosion accompanied increased total chemical erosion in ice free areas consideration of the maximum possible effect of meltwater at ice margins leads to an 80 increase in the global chemical erosion rate at 18 ka such an increase would lead to a larger and faster drop in atmospheric pco2 but also to an excessive deepening of the global ccd this scenario seems unrealistic our results are contrary to interpretations of a much higher silicate chemical erosion rate during glaciations based on recently published records of quaternary marine sr isotopic ratios therefore if these records are indeed globally representative and entirely due to increased silicate chemical erosion as opposed to changes in source areas or hydrothermal inputs then other factors such as a shift in the global weathering regime which we do not explicitly consider here may be involved sensitivity tests show that considering spatial heterogeneities in lithology and runoff leads to lower predictions of global chemical erosion rates than what one would obtain by considering only global averages in a non spatially resolved calculation

north atlantic ventilation of southern sourced deep water in the glacial ocean one potential mechanism for lowering atmospheric co2 during glacial times is an increase in the fraction of the global ocean ventilated by the north atlantic which produces deep water with a low concentration of unused nutrients and thus drives the ocean s biological pump to a high efficiency however the data indicate that during glacial times a water mass low in 13c 12c and 14c c occupied the deep atlantic apparently at the expense of north atlantic deep water nadw this water is commonly referred to as southern sourced because of its apparent entry into the atlantic basin from the south prompting the inference that it was ventilated at the southern ocean surface here we propose that this deep atlantic water mass actually included a large fraction of north atlantic ventilated water the chemical characteristics of which were altered by recirculation in the deep southern and indo pacific oceans in an ocean model sensitivity experiment that reduces antarctic bottom water formation and weakens its overturning circulation we find that a much greater fraction of nadw is transported into the southern ocean without contacting the surface and is entrained and mixed into the southern sourced deep water that spreads into the global abyssal ocean thus north atlantic ventilation takes over more of the ocean interior lowering atmospheric co2 and yet the abyssal atlantic is filled from the south with old water low in 13c 12c and 14c c consistent with glacial data

carbonate dissolution fluctuations in the western equatorial pacific during the late quaternary planktonic foraminiferal test fragmentation in three cores along a depth transect from the western equatorial pacific erdc 93p 1619 m rc17 177 2600 m v28 238 3120 m thompson 1976 were examined for the last 500 kyr at sample intervals from 2 5 to 5 kyr to study the fluctuations of dissolution in the western equatorial pacific the age models were constructed by correlating the 18o records with the specmap stack imbrie et al 1984 results showed that intermediate and deep waters experienced the same patterns of dissolution through climatic cycles fragmentation varied with a greater amplitude and the carbonate ion concentration changed less in the deep than in the intermediate water dissolution has significant variance distributions and coherencies with 18o over the 100 41 and 23 kyr periods of orbital variations dissolution maxima lag ice volume minima by 6 to 20 kyr the dissolution variability was consistent with recent geochemical models which seek to explain the reduction of atmospheric co2 concentration at the last glacial maximum broecker 1982 boyle 1988

cretaceous pacific plate movement beneath se china evidence from episodic volcanism and related intrusions abstract extensive late mesozoic igneous rocks in se china have been widely considered to be generated under the paleo pacific tectonic regime the plate subduction model however remains controversial this study focuses on the cretaceous volcanic rocks in northwestern zhejiang province zircon u pb age determination indicates that cretaceous volcanism in northwestern zhejiang took place at three episodes of 140 130 130 127 and 123 118 ma in good agreement with the coeval lower volcanic series in southeastern zhejiang but lacking the episode at 110 88 ma corresponding to the upper volcanic series the cretaceous volcanic rocks in zhejiang therefore show an oceanward younging trend in situ zircon hf isotope analyses of three episodes of volcanics yield e hf t values of 11 2 to 8 7 4 8 to 2 4 and 4 4 to 2 2 respectively the entire sequences display typical isotopic features of magma mixing implying progressive involvement of juvenile component based on systematical researches on the cretaceous volcanic rocks and a series of granitoid plutons in zhejiang it is also identified that the juvenile component involvement gradually occurred from the inland to the coast under an enhanced lithospheric extensional tectonic setting all the observations in this study indicate the northwestward paleo pacific plate subduction with episodic slab rollback which triggered the arc system to retreat towards the pacific ocean rather than the southwestward subduction related to the ridge subduction along the lower yangtze river belt

biogenic budgets of particle rain benthic remineralization and sediment accumulation in the equatorial pacific abstract budgets of organic c corg cac03 and opal have been constructed for the palisades ny pacific equatorial region at 140 w between 5 n and 5 s measurements of the rain and benthic remineralization rate of biogenic materials have been adjusted and normalized to account for sampling biases sea surface temperature serves as a master variable in normalizing sediment trap and benthic remineralization data to average conditions the rain and remineralization rates for corg are nearly equal 0 40 0 05 and 0 46 0 06 mmol m 2 d 1 respectively thus only a minor fraction of this constituent is buried rain and dissolution rates for biogenic opal are similarly balanced 0 3 0 06 and 0 36 0 01 mmol m 2 d 1 and consistent with the value for opal burial 0 0 0 004 the cac03 budget appears to have changed during the holocene the best estimates of modern cac03 dissolution 0 58 0 03 mmol m 2 d 1 and rain rate 0 61 0 06 are consistent with230th normalized carbonate accumulation rates for the late holocene 0 1 mmol m 2 d 1 however the balance between dissolution and rain is not consistent with early holocene carbonate accumulation 0 3 mmol m 2 d 1 and this imbalance suggests 1 a recent increase in the rate of cac03 dissolution on the sea floor or 2 a decrease in the rain rate of carbonate particles modeling230th profiles in sediments from this region define the last 3000 years as the duration of increased dissolution or decreased particle rain 231pa 230th ratios in sediments indicate that particle rain rates have remained constant or possibly increased slightly through the holocene two potential causes for increased dissolution were investigated a change in deep water carbonate saturation or a change in co g cac03 rain ratios a model describing carbonate dissolution as a function of the degree of undersaturation and the amount of organic carbon oxidation within sediments indicates that the recent increase in dissolution is more likely due to changes in bottom water chemical composition we propose that pacific ocean bottom water carbonate ion concentration has decreased by 10 15 m over the last 3000 years

paired benthic foraminiferal cd ca and zn ca evidence for a greatly increased presence of southern ocean water in the glacial north atlantic benthic foraminiferal 13c and cd ca studies suggest that deep atlantic circulation during the last glacial maximum was very different from today with high nutrient low 13c high cd deep southern ocean water sow penetrating far into the north atlantic however if some glacial 13c values are biased by productivity artifacts and or air sea exchange processes then the existing 13c data may be consistent with the continual dominance of north atlantic deep water nadw cibicidoides wuellerstorfi cd ca results presented here indicate that the glacial north atlantic was strongly enriched in dissolved cd below 2500 m depth if nadw formation was still vigorous relative to sow formation these data could be explained by either increased preformed nutrient levels in the high latitude north atlantic or by increased organic matter remineralization within lower nadw high glacial zn ca values in the same samples however are best explained by a substantially increased mixing with zn rich sow the cause was most likely a partial replacement of nadw by less dense glacial north atlantic intermediate water this reorganization also lowered deep north atlantic co32 concentrations by perhaps 10 to 15 mol kg 1

seawater carbonate ion δ13c systematics and application to glacial interglacial north atlantic ocean circulation seawater carbonate ion and 13c are affected by many processes including biology air sea exchange alkalinity change and mixing between different water masses study of modern ocean data shows that deep ocean carbonate ion and 13c of dissolved inorganic carbon can be used together as useful tracers for deep water mass reconstructions in the past we present records of deep water carbonate ion concentration co32 changes of the north atlantic ocean water column since the last glacial quantitatively reconstructed using benthic foraminiferal boron calcium b ca ratios records from six cores over 1 to 4 km reveal that the carbonate chemistry of the glacial north atlantic was more stratified than the modern ocean with higher co32 by 20 30 mol kg 1 at 1 2 km and lower co32 by 20 mol kg 1 at sites deeper than 3 5 km producing an 800 m glacial shoaling of calcite saturation horizon comparison with benthic foraminiferal 13c and var epsilonnd of fe mn oxide leachates shows that the deep glacial waters with low co32 are consistent with a southern ocean source while those with high co32 but distinct 13c chemistry were supplied by two endemic sources one being the norwegian greenland sea ngs our carbonate ion results suggest that the glacial boundary between north and south sourced deep waters is at 2 8 km significantly deeper than 2 3 km estimated from benthic foraminiferal 13c weakened surface compensation inflow to the ngs promoted cooling and continental ice growth at north high latitude and a deeper boundary may reduce atmospheric co2 sequestration in the deep atlantic implying a greater role of other parts of the ocean

variations in mg ca and sr ca ratios of planktonic foraminifera caused by postdepositional dissolution evidence of shallow mg dependent dissolution a comparative study has been made of two species of planktonic foraminifera g tumida and g sacculifer in a depth transect on the ontong java plateau western equatorial pacific g tumida tests from core top sediments showed decreasing mg ca 2 65 1 25 mmol mol and sr ca 1 50 1 16 mmol mol ratios with increasing water depth 1600 4400 m while no such variation was found in g sacculifer tests in excess of 355 m average mg ca 3 6 mmol mol sr ca 1 4 mmol mol artificial dissolution of g tumida tests led to a decrease in both mg ca and sr ca but in g sacculifer there was no significant change in the ratios analyses by electron microprobe revealed that mg ca of the inner chamber calcite in g tumida tests was much higher than that of the calcite crust keel whereas sr ca was only slightly elevated there were no consistent spatial differences in either mg ca or sr ca for g sacculifer tests dissolution in the oceans gives rise to the removal of the chamber calcite in g tumida about 30 of the total calcite leaving the keel calcite although g tumida is thought of as a dissolution resistant form the majority of mg ca and sr ca depletion and chamber loss occurs above the lysocline it is also possible that much of the mg enriched gametogenic calcite has been lost by dissolution from g sacculifer above 1600 m mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera calculations show that the saturation horizon for mg rich parts of tests may be elevated by several hundred meters compared with normal calcite

preferential dissolution of benthic foraminiferal calcite during laboratory reductive cleaning we have investigated the effect of cleaning procedures on eight element ca ratios in three widely used benthic foraminifera species from core top and down core sediments two cleaning techniques were employed 1 comparison between mg cleaning and cd cleaning methods and 2 comparison between the various constituent reagents li ca b ca and sr ca ratios remained unchanged for samples subjected to different treatments but mg ca mn ca zn ca cd ca and u ca were substantially decreased when foraminifera shells were cleaned with reagents containing citrate in contrast no significant decreases in element ca ratios were observed for samples cleaned in n2h4 without citrate indicating that the role of n2h4 was insignificant during reductive cleaning and that citrate is responsible for decreases of mg ca mn ca zn ca cd ca and u ca decreases in these ratios are most likely due to 1 removal of contaminant particles enriched in mg mn zn cd and u and or 2 preferential leaching of caco3 by the formation of stable metal complexes through chelation between citrate and metals heterogeneously distributed in foraminiferal shells due to the negligible effect of n2h4 and preferential dissolution of caco3 during reductive cleaning it is suggested that the reductive cleaning step should be omitted and the mg cleaning method barker et al 2003 could be employed to clean foraminiferal shells for trace element measurements

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

calibration of the boron isotope proxy in the planktonic foraminifera globigerinoides ruber for use in palaeo co2 reconstruction abstract the boron isotope ph proxy applied to mixed layer planktic foraminifera has great potential for estimating past co2 levels which in turn is crucial to advance our understanding of how this greenhouse gas influences earth s climate previous culture experiments have shown that although the boron isotopic compositions of various planktic foraminifera are ph dependent they do not agree with the aqueous geochemical basis of the proxy here we outline the results of culture experiments on globigerinoides ruber white across a range of ph 7 5 8 2 and analysed via multicollector inductively coupled plasma mass spectrometry mc icpms and compare these data to core top and sediment trap samples to derive a robust new species specific boron isotope ph calibration consistent with earlier culture studies we show a reduced ph dependency of the boron isotopic composition of symbiont bearing planktonic foraminifera compared to borate ion in seawater we also present evidence for a size fraction effect in the 11b of g ruber finally we reconstruct atmospheric co2 concentrations over the last deglacial using our new calibration at two equatorial sites odp site 999a and site geob1523 1 these data provide further grounding for the application of the boron isotope ph proxy in reconstructions of past atmospheric co2 levels

rapid coupling between ice volume and polar temperature over the past 150 000 years a new approach to dating a continuous sea level record using speleothem u th ages shows that past variations in global ice volume occurred within centuries of polar climate change with rates of sea level rise reaching at least 1 metre per century

carbon dioxide effects of antarctic stratification north atlantic intermediate water formation and subantarctic nutrient drawdown during the last ice age diagnosis and synthesis in a geochemical box model in a box model synthesis of southern ocean and north atlantic mechanisms for lowering co2 during ice ages the co2 changes are parsed into their component geochemical causes including the soft tissue pump the carbonate pump and whole ocean alkalinity when the mechanisms are applied together their interactions greatly modify the net co2 change combining the antarctic mechanisms stratification nutrient drawdown and sea ice cover within bounds set by observations decreases co2 by no more than 36 ppm a drawdown that could be caused by any one of these mechanisms in isolation however these antarctic changes reverse the co2 effect of the observed ice age shoaling of north atlantic overturning in isolation the shoaling raises co2 by 16 ppm but alongside the antarctic changes it lowers co2 by an additional 13 ppm a 29 ppm synergy the total co2 decrease does not reach 80 ppm partly because antarctic stratification antarctic sea ice cover and the shoaling of north atlantic overturning all strengthen the sequestration of alkalinity in the deepest ocean which increases co2 both by itself and by decreasing whole ocean alkalinity increased nutrient consumption in the sub antarctic causes as much as an additional 35 ppm co2 decrease interacting minimally with the other changes with its inclusion the lowest ice age co2 levels are within reach these findings may bear on the two stepped co2 decrease of the last ice age

glacial interglacial variability in the delivery of dust to the central equatorial pacific ocean abstract fluxes of continental mineral aerosols dust were greater during glacial periods than during interglacials throughout most regions of the earth the equatorial pacific ocean was a possible exception to this pattern in that previous studies have reported either greater dust fluxes during interglacials or no consistent glacial interglacial pattern of dust flux we have applied the 230th normalization technique to derive five new records of dust flux from central equatorial pacific ocean sediments in contrast to previous studies which relied on stratigraphic accumulation rates the 230th normalization technique produces internally consistent results revealing fluxes to this region of continental lithogenic material that were positively correlated with global ice volume throughout the past 300 000 yr maximum glacial fluxes of continental mineral aerosols exceed minimum interglacial fluxes by about a factor of 2 similar to changes found elsewhere at low and mid latitudes this amplitude of variability is substantially smaller than that seen in some recent models and these observations provide a calibration point for future model development

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

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

subarctic pacific evidence for a glacial deepening of the oceanic respired carbon pool abstract measurements of benthic foraminiferal cadmium calcium cd ca have indicated that the glacial interglacial change in deep north pacific phosphate po4 concentration was minimal which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean here we present sedimentary redox sensitive trace metal records from ocean drilling program odp site 882 nw subarctic pacific water depth 3244 m to make inferences about changes in deep north pacific oxygenation and thus respired carbon storage over the past 150 000 yr these observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment our results suggest that the deep subarctic pacific water mass was depleted in oxygen during glacial maxima though it was not anoxic we reconcile our results with the existing benthic foraminiferal cd ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed rather than remineralized this change would have corresponded to an increase in the deep pacific storage of respired carbon which would have lowered atmospheric carbon dioxide co2 by sequestering co2 away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea the magnitude of change in preformed nutrients suggested by the north pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pco2

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

lowering of glacial atmospheric co2 in response to changes in oceanic circulation and marine biogeochemistry 1 we use an earth system model of intermediate complexity climber 2 to investigate what recent improvements in the representation of the physics and biology of the glacial ocean imply for the atmospheric concentration the coupled atmosphere ocean model under the glacial boundary conditions is able to reproduce the deep salty stagnant water mass inferred from antarctic deep pore water data and the changing temperature of the entire deep ocean when carbonate compensation is included in the model we find a co2 drawdown of 43 ppmv associated mainly with the shoaling of the atlantic thermohaline circulation and an increased fraction of water masses of southern origin in the deep atlantic fertilizing the atlantic and indian sectors of the southern ocean north of the polar front leads to a further drawdown of 37 ppmv other changes to the glacial carbon cycle include a decrease in the amount of carbon stored in the terrestrial biosphere 540 pg c which increases atmospheric co2 by 15 ppmv and a change in ocean salinity resulting from a drop in sea level which elevates co2 by another 12 ppmv a decrease in shallow water caco3 deposition draws down co2 by 12 ppmv in total the model is able to explain more than two thirds 65 ppmv of the glacial to interglacial co2 change based only on mechanisms that are clearly documented in the proxy data a good match between simulated and reconstructed distribution of 13c changes in the deep atlantic suggests that the model captures the mechanisms of reorganization of biogeochemistry in the atlantic ocean reasonably well additional poorly constrained mechanisms to explain the rest of the observed drawdown include changes in the organic carbon caco3 ratio of sediment rain reaching the seafloor iron fertilization in the subantarctic pacific ocean and changes in terrestrial weathering

a need to improve reconstructions of the fluctuations in the calcite compensation depth over the course of the cenozoic reconstructions based on back tracked depths of the transition between caco3 bearing and caco3 depleted sediment suggest that over the last 65 million years the ocean s caco3 compensation depth ccd has remained within the range 4 0 0 6 km taken at face value these results indicate that depth of the calcite saturation horizon and hence also the product of the ca and co3 concentrations have remained nearly constant in turn this suggests that the ratio of calcite production to ingredient supply has not undergone large changes in this paper the method used to reconstruct the temporal fluctuations and interocean differences in the depth of the calcite saturation horizon is scrutinized the basis for my concern is that offset between the depth of the calcite saturation horizon and the depth where dissolution reduces the caco3 content to 20 i e the ccd can vary by a half kilometer or so depending on the rain rates of caco3 and non caco3 when observations on modern ocean sediments are used to test the reliability of these reconstructions the result is that when averaged over a full glacial cycle the depth of the ccds in the pacific and indian oceans fall within the long term range reliable documentation of fluctuations around this long term average requires that additional measurements such as extent of fragmentation be used to supplement those of caco3 content

abyssal atlantic circulation during the last glacial maximum constraining the ratio between transport and vertical mixing transport to vertical diffusivity in the deep atlantic our calculations suggest that the ratio was at least twice as large at the lgm we speculate that the primary cause was reduced mixing between northern and southern component waters associated with movement of this water mass boundary away from the zone of intense mixing near the seafloor the shallower water mass boundary yields an order of magnitude increase in the volume of southern component water suggesting its residence time may have increased substantially our analysis supports the idea that an expanded volume of antarctic bottom water and limited vertical mixing enhanced the abyssal ocean s ability to trap carbon during glacial times

no evidence for a deglacial intermediate water δ14c anomaly in the sw atlantic abstract the last deglaciation was characterized by an increase in atmospheric pco 2 and decrease in atmospheric radiocarbon activity one hypothesis is that these changes were due to out gassing of 14 c depleted carbon from the abyssal ocean reconstructions of foraminiferal 14 c from the eastern tropical pacific arabian sea and high latitude north atlantic show that severe depletions in 14 c occurred at intermediate water depths during the last deglaciation it has been suggested that 14 c depleted water from the abyss upwelled in the southern ocean and was then carried by antarctic intermediate water aaiw to these sites however locations in the south pacific in the direct path of modern day aaiw do not exhibit the 14 c excursion and therefore cast doubt upon the aaiw mechanism de pol holz et al 2010 rose et al 2010 here we evaluate whether or not a deglacial 14 c anomaly occurred at intermediate depths in the southwest atlantic we find that the deglacial benthic 14 c trend at our site is similar to the atmospheric 14 c trend our results are also largely consistent with results from u th dated corals at shallower water depths on the brazil margin mangini et al 2010 we find no evidence in the southwestern atlantic of a 300 decrease in intermediate water 14 c from 18 to 14 kyr bp like that observed in the eastern tropical pacific marchitto et al 2007 when our results are paired with those from the south pacific it appears aaiw did not carry a highly 14 c depleted signal during the deglaciation another source of carbon is apparently required to explain the intermediate depth 14 c anomalies in the north atlantic indian and pacific oceans

determination of multiple element calcium ratios in foraminiferal calcite by quadrupole icp ms a method has been developed for rapid and precise simultaneous determination of nine element ca ratios in foraminiferal tests directly from intensity ratios using external matrix matched standards on a quadrupole inductively coupled plasma mass spectrometer icp ms all quantification isotopes are determined in pulse mode to avoid cross calibration small argide 40ar26mg interferences on 66zn are corrected by using two additional mg and zn standards a stable signal conducive for high precision measurements is obtained by cone conditioning variable calcium concentration has negligible effect on li al mn and sr but ca concentrations for standards and samples need to be constrained at a similar level for precise measurements of zn cd and u aliquots of samples are first analyzed for ca concentrations on an inductively coupled plasma atomic emission spectrometer icp aes and the remaining solutions are diluted to ca concentration of 100 ppm for ratio measurements to assure data quality the long term reproducibility of the method yielded precisions of li ca 2 4 b ca 4 2 mg ca 1 4 al ca 14 mn ca 0 9 zn ca 2 8 1 2 7 8 mol mol and 5 1 0 5 1 2 mol mol sr ca 0 9 cd ca 2 4 0 07 0 24 mol mol and 4 8 0 01 0 07 mol mol and u ca 2 5 for foraminiferal samples as small as 60 g

the southern ocean s role in carbon exchange during the last deglaciation changes in the upwelling and degassing of carbon from the southern ocean form one of the leading hypotheses for the cause of glacial interglacial changes in atmospheric carbon dioxide we present a 25 000 year long southern ocean radiocarbon record reconstructed from deep sea corals which shows radiocarbon depleted waters during the glacial period and through the early deglaciation this depletion and associated deep stratification disappeared by 14 6 ka thousand years ago consistent with the transfer of carbon from the deep ocean to the surface ocean and atmosphere via a southern ocean ventilation event given this evidence for carbon exchange in the southern ocean we show that existing deep ocean radiocarbon records from the glacial period are sufficiently depleted to explain the 190 per mil drop in atmospheric radiocarbon between 17 and 14 5 ka

sampling statistic limitations on benthic foraminifera chemical and isotopic data abstract analyses of benthic foraminiferal isotopic and chemical properties are typically done on a small number of individuals often 5 10 because benthic sediment mixing produces a mix of individuals whose properties were determined at times encompassing several thousand years a sampling of several individuals does not adequately represent the average mixture a quantitative statistical analysis shows that this effect places a fundamental limit on measurement precision in cores especially where rapid environmental changes occur over short vertical distances the fundamental parameters defining this limit are the rate of change of the property per unit distance and the effective mixing depth in cores found in the vema channel rio grande rise region where sedimentation rates are about 1 cm ka 1 and mixing depths are about 3 cm a single sampling of six individuals can produce a result that has an expected one sigma standard deviation of 6 25 of the observed range precision can be improved by using more individuals or running more replicate analyses but the result only improves as the square root of the number of individuals or replicates this effect is illustrated by cd ca and isotopic data from low 0 7 cm ka 1 and moderate 1 5 cm ka 1 sedimentation rate cores although precision is compromised the most in low sedimentation rate cores this effect contributes to imprecision in high sedimentation rate cores as well