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

modelling the geochemical cycle of boron implications for the long term δ11b evolution of seawater and oceanic crust the boron geochemical cycle has been simulated using a time dependent geochemical box model that was coupled to a onedimension model of seawater oceanic crust interactions boron elemental and isotopic compositions of oceanic rocks as a function of depth were calculated by mass balance using the temperature and porosity profiles of the crust as well as the available experimental and empirical distribution coefficients and fractionation factors between mineral and water ranges of boron elemental and isotopic variations of seawater were calculated for crust seawater interactions that take place from the ridge axis to the off axis closure of the hydrothermal system the present day d11b of seawater 40 could represent a steady state value however depending on crustal permeability lifetime of water rock interactions and expansion rate of the oceanic ridge the d11b of seawater may vary from 30 to 50 at the 10 million year scale some boron isotope compositions of cretaceous biogenic carbonates and ophiolitic serpentinites from oman are comparable to modern rock samples suggesting that the d11b of cretaceous seawater was close to the present day value low d11b values of some biogenic carbonates cannot be attributed to low ph values of past seawater but more probably to d11b variations of seawate or diagenetic alteration by crustal aqueous fluids boron isotope composition of hydrothermally altered serpentines could be considered as a promising proxy of the seawater composition

seawater ph pco2 and co2 3 variations in the caribbean sea over the last 130 kyr a boron isotope and b ca study of planktic foraminifera abstract here a new analytical methodology is described for measuring the isotopic composition of boron in foraminifera using multicollector inductively coupled plasma mass spectrometry mc icpms this new approach is fast 10 samples analysed in duplicate per analytical session and accurate to better than 0 25 at 95 confidence with acceptable sample size requirements 1 3 mg of carbonate a core top calibration of several common planktic and two benthic species from geographically widespread localities shows a very close agreement between the isotopic composition measured by mc icpms and the isotopic composition of b oh 4 in seawater as predicted using the recently measured isotopic equilibrium factor of 1 0272 at the depth of habitat a down core and core top investigation of boron concentration b ca ratio shows that the partition coefficient is influenced by co2 3 complicating the application of this proxy nevertheless it is demonstrated that these two proxies can be used to fully constrain the carbonate system of surface water in the caribbean sea odp site 999a over the last 130 kyr this reconstruction shows that during much of the holocene and the last interglacial period surface water at site 999a was in equilibrium with the atmosphere with respect to co2 during the intervening colder periods although the surface water pco2 was lower than the holocene it was a minor to significant source of co2 to the atmosphere possibly due to either an expansion of the eastern equatorial atlantic upwelling zone or a more local expansion of coastal upwelling in the southern caribbean such reorganisation of the oceanic carbonate system in favour of a larger source of co2 to the atmosphere from the equatorial ocean may require mechanisms responsible for lowering atmospheric co2 during glacial periods to be more efficient than previously supposed

a cenozoic record of the equatorial pacific carbonate compensation depth atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks these feedbacks involve the erosion of silicate rocks and organic carbon bearing rocks the integrated effect of these processes is reflected in the calcium carbonate compensation depth which is the oceanic depth at which calcium carbonate is dissolved here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial pacific ocean the carbonate compensation depth tracks long term ocean cooling deepening from 3 0 3 5 kilometres during the early cenozoic approximately 55 million years ago to 4 6 kilometres at present consistent with an overall cenozoic increase in weathering we find large superimposed fluctuations in carbonate compensation depth during the middle and late eocene using earth system models we identify changes in weathering and the mode of organic carbon delivery as two key processes to explain these large scale eocene fluctuations of the carbonate compensation depth

comment on significance of apatite ree depletion and monazite inclusions in the brecciated sehchahun iron oxide apatite deposit bafq district iran insights from paragenesis and geochemistry by bonyadi z davidson g j mehrabi b meffre s ghazban f chem geol 281 253 269 abstract in contrast to the ill defined iocgs model the rapitan type bifs of neoproterozoic age are characterized by their distinct association with glaciogenic diamictite rich jaspilites the late neoproterozoic early paleozoic rapitan type sehchahun magnetite jaspilite apatite mineralization is hosted by a brecciated proximal zone of magnetite bearing keratophyres and a distal zone of diamictite rich jaspilites the titanium values in magnetite are imprecise and highly variable due to the oxidation of magnetites the high values of titanium are attributed to the tin and niobium rich rutile rather than the equilibrated ilmenite exsolution textures the values of f sr and mn in apatites are similar to those of the sedimentary apatites remobilized by hydrothermal fluids during rhyolitic submarine volcanism the presence of keratophyres jaspilites diamictites dropstones and phosphorous geochemistry in sehchahun deposit has the best correlation with rapitan type banded iron phosphorous formations rather than a fragile model of iocg ore the main argument against the iocg model of bonyadi et al 2011 is that the model has never ever been reported to be associated with jaspilites and diamictites

foredeeps versus subduction zones the geologic characteristics of foredeeps and accretionary wedges suggest that these features are distinguishable on the basis of the direction of the associated subduction east north east dipping subduction related accretionary wedges show high relief and broad outcrops of metamorphic rocks they are associated with shallow foredeeps with low subsidence rates in contrast west dipping subduction related accretionary wedges show low relief and involve mainly sedimentary cover the related foredeeps are deep and have high subsidence rates this differentiation is useful both for oceanic and continental subductions e g eastern vs western pacific subductions or east dipping alpine vs west dipping apenninec subductions in a cross section of the alps the ratio of the area of the orogen to the area of the foredeeps is at least 2 1 whereas this ratio is 0 22 1 for the apennines these ratios explain why foredeeps related to east or northeast dipping subduction are quickly filled and are bypassed by clastic rocks whereas foredeeps related to west dipping subduction maintain a deep water environment longer these differences support the presence of an eastward asthenospheric counterflow relative to the westward drift of the lithosphere detected in the hot spot reference frame even in the mediterranean where no hot spots are present in this interpretation the apennines foredeep was caused by the eastward push of the mantle acting on the subducted slab whereas the foredeeps in the alps were caused by the load of the thrust sheets and the downward component of movement of the upper adriatic plate these forces contrast with the upward component of the eastward mantle flow

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

sea level sediments and the composition of seawater the composition of seawater changed significantly during the course of the phanerozoic in concert with long term changes in sea level which were largely the result of changes in the volume of mid ocean ridges these reflect changes in the rate of seafloor spreading and determine the rate of seawater cycling through mid ocean ridges spencer and hardie 1990 and hardie 1996 proposed that the changes in the cycling rate of seawater through mid ocean ridges have been responsible for the changes in the composition of seawater during the phanerozoic this explanation cannot account for the major changes in the composition of seawater during the cenozoic which was a time of nearly constant seafloor spreading rate however changes in the rate of deposition of shallow water carbonates and their penecontemporaneous dolomitization can explain the cenozoic changes in seawater composition this indicates that sedimentologic parameters have played a major role in the chemical evolution of seawater the more rapid cycling of seawater through mors during the mesozoic can explain semiquantitatively the fairly minor differences between the composition of seawater in the eocene and in the jurassic changes in the composition of seawater during the paleozoic were probably determined both by changes in the rate of dolomite and gypsum anhydrite deposition and by changes in the rate of seawater cycling through mid ocean ridges if the causes of these compositional changes are the same as those during the cenozoic and mesozoic then sedimentologic factors have been significantly more important than the rate of cycling of seawater through mors in shaping the chemical evolution of seawater during the phanerozoic

rapid and sustained surface ocean acidification during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm has been associated with the release of several thousands of petagrams of carbon pg c as methane and or carbon dioxide into the ocean atmosphere system within 10 kyr on the basis of the co occurrence of a carbon isotope excursion cie widespread dissolution of deep sea carbonates and global warming in theory this rapid carbon release should have severely acidified the surface ocean though no geochemical evidence has yet been presented using boron based proxies for surface ocean carbonate chemistry we present the first observational evidence for a drop in the ph of surface and thermocline seawater during the petm planktic foraminifers from a drill site in the north pacific ocean drilling program site 1209 show a 0 8 decrease in boron isotopic composition 11b at the onset of the event along with a 30 40 reduction in shell b ca similar trends in 11b are present in two lower resolution records from the south atlantic and equatorial pacific these observations are consistent with significant global acidification of the surface ocean lasting at least 70 kyr and requiring sustained carbon release the anomalies in the b records are consistent with an initial surface ph drop of 0 3 units at the upper range of model based estimates of acidification

calcium and magnesium isotope systematics in rivers draining the himalaya tibetan plateau region lithological or fractionation control abstract in rivers draining the himalaya tibetan plateau region the 26mg 24mg ratio has a range of 2 and the 44ca 42ca ratio has a range of 0 6 the average 26 mg values of tributaries from each of the main lithotectonic units tethyan sedimentary series tss high himalayan crystalline series hhcs and lesser himalayan series lhs are within 2 standard deviation analytical uncertainty 0 14 the consistency of average riverine 26 mg values is in contrast to the main rock types limestone dolostone and silicate which range in their average 26 mg values by more than 2 tributaries draining the dolostones of the lhs differ in their 44 42 ca values compared to tributaries from the tss and hhcs the chemistry of these river waters is strongly influenced by dolostone solute mg ca close to unity and both 26 mg 1 31 and 44 42 ca 0 64 values are within analytical uncertainty of the lhs dolostone these are the most elevated 44 42 ca values in rivers and rock reported so far demonstrating that both riverine and bedrock 44 42 ca values may show greater variability than previously thought although rivers draining tss limestone have the lowest 26 mg and 44 42 ca values at 1 41 and 0 42 respectively both are offset to higher values compared to bedrock tss limestone the average 26 mg value of rivers draining mainly silicate rock of the hhcs is 1 25 lower by 0 63 than the average silicate rock these differences are consistent with a fractionation of 26 mg values during silicate weathering given that the proportion of mg exported from the himalaya as solute mg is small the difference in 26mg 24mg ratios between silicate rock and solute mg reflects the 26mg 24mg isotopic fractionation factor silicate dissolved mg between silicate and dissolved mg during incongruent silicate weathering the value of silicate dissolved mg of 0 99937 implies that in the tss solute mg is primarily derived from silicate weathering whereas the source of ca is overwhelmingly derived from carbonate weathering the average 44 42 ca value in hhcs rivers is within uncertainty of silicate rock at 0 39 the widespread hot springs of the high himalaya have an average 26 mg value of 0 46 and an average 44 42 ca value of 0 5 distinct from riverine values for 26 mg but similar to riverine 44 42 ca values although rivers draining each major rock type have 44 42 ca and 26 mg values in part inherited from bedrock there is no correlation with proxies for carbonate or silicate lithology such as na ca ratios suggesting that ca and mg are in part recycled however in spite of the vast contrast in vegetation density between the arid tibetan plateau and the tropical lesser himalaya the isotopic fractionation factor for ca and mg between solute and rocks are not systematically different suggesting that vegetation may only recycle a small amount of ca and mg in these catchments the discrepancy between solute and solid ca and mg isotope ratios in these rivers from diverse weathering environments highlight our lack of understanding concerning the origin and subsequent path of ca and mg bound as minerals in rock and released as cations in rivers the fractionation of ca and mg isotope ratios may prove useful for tracing mechanisms of chemical alteration ca isotope ratios of solute riverine ca show a greater variability than previously acknowledged the variability of ca isotope ratios in modern rivers will need to be better quantified and accounted for in future models of global ca cycling if past variations in oceanic ca isotope ratios are to be of use in constraining the past carbon cycle

paleomagnetic evidence for a neogene two phase counterclockwise tectonic rotation in the northern apennines italy paleomagnetic directions have been determined for a new collection of early oligocene and late miocene pliocene epiligurian clastic sediments from the frontal portions of the northern apennines these results are combined with cenozoic data from the literature to evaluate whether rotations of units in this region are related to the oligomiocene corsica sardinia rotation and or to younger phases of deformation of the apennine chain when corsica sardinia moved counterclockwise ov the coast of france the ligurian units located at its front were presumably pushed eastward and rotated counterclockwise above a main boundary thrust onto the adria africa margin we propose that about 24 out of a total of 52 of rotation observed in the epiligurian units can be related to the oligo miocene motion of the corsica sardinia block in partial agreement with previous conclusions and the remaining 28 to the pliocene tectonic phase at the apennine chain front which may have re activated thrust planes in the adria africa succession below the ligurian wedge 2000 elsevier science b v all rights reserved

boron and magnesium isotopic composition of seawater the isotopic systems of boron and magnesium are increasingly being used as proxies for a number of environmental variables and processes the isotopic composition of seawater for both systems plays a central role in these studies and is an important interlaboratory standard given the long residence times of both elements 10 7 years it is commonly assumed that seawater is isotopically homogenous for these systems yet no systematic studies currently exist here we present the b and mg isotopic composition of 26 28 seawater samples from a number of ocean basins that encompass a significant range in salinity 32 to 38 psu temperature 0 3 to 25 9c and water depth 0 to 1240 m we find no significant or systematic variation for either system in accordance with their long residence times we recommend that the mean values we report 11 b 39 61 0 04 2 s e n 28 25 mg 0 43 0 01 2 s e n 26 26 mg 0 82 0 01 2 s e n 26 be used in future studies involving mg and b isotopes copyright 2010 by the american geophysical union

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

atmospheric carbon dioxide through the eocene oligocene climate transition geological and geochemical evidence1 2 3 indicates that the antarctic ice sheet formed during the eocene oligocene transition4 33 5 34 0 million years ago modelling studies5 6 suggest that such ice sheet formation might have been triggered when atmospheric carbon dioxide levels fell below a critical threshold of 750 p p m v but the timing and magnitude of relative to the evolution of the ice sheet has remained unclear here we use the boron isotope ph proxy7 8 on exceptionally well preserved carbonate microfossils from a recently discovered geological section in tanzania9 10 to estimate before during and after the climate transition our data suggest that a reduction in occurred before the main phase of ice growth followed by a sharp recovery to pre transition values and then a more gradual decline during maximum ice sheet growth was between 450 and 1 500 p p m v with a central estimate of 760 p p m v the ice cap survived the period of recovery although possibly with some reduction in its volume implying as models predict11 a nonlinear response to climate forcing during melting overall our results confirm the central role of declining in the development of the antarctic ice sheet in broad agreement with carbon cycle modelling12 and help to constrain mechanisms and feedbacks associated with the earth s biggest climate switch of the past 65 myr

causes of ice age intensification across the mid pleistocene transition during the mid pleistocene transition mpt 1 200 800 kya earth s orbitally paced ice age cycles intensified lengthened from 40 000 40 ky to 100 ky and became distinctly asymmetrical testing hypotheses that implicate changing atmospheric co2 levels as a driver of the mpt has proven difficult with available observations here we use orbitally resolved boron isotope co2 data to show that the glacial to interglacial co2 difference increased from 43 to 75 atm across the mpt mainly because of lower glacial co2 levels through carbon cycle modeling we attribute this decline primarily to the initiation of substantive dust borne iron fertilization of the southern ocean during peak glacial stages we also observe a twofold steepening of the relationship between sea level and co2 related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase locking we argue that neither ice sheet dynamics nor co2 change in isolation can explain the mpt instead we infer that the mpt was initiated by a change in ice sheet dynamics and that longer and deeper post mpt ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the southern ocean as a consequence of larger ice sheets

the universal ratio of boron to chlorinity for the north pacific and north atlantic oceans abstract we report seawater boron concentration mg kg 1 and chlorinity values measured in seawater samples n 139 collected at various depths in the north pacific and north atlantic oceans and the east japan sea located in the western temperate north pacific our results indicate that variations in seawater boron concentration are strongly coupled to variations in chlorinity and salinity yielding a mean boron to chlorinity ratio of 0 2414 0 0009 mg kg 1 1 boron to salinity ratio 0 1336 0 0005 mg kg 1 1 this ratio was surprisingly universal throughout the water column in the three marine basins and across widely different ocean surface regimes but differs from the generally accepted ratio of 0 232 0 005 mg kg 1 1 determined by uppstrom 1974 which was based on only 20 measurements at four sites in the tropical pacific ocean in converting total alkalinity to carbonate alkalinity and vice versa for thermodynamic calculations the difference between these two ratios leads to a difference of 5 mol kg 1 in estimates for ocean surface waters where the contribution of borate to total alkalinity is typically greatest we suggest the use of the new boron to chlorinity ratio for predicting seawater boron concentrations using chlorinity or salinity data

structural textural geochemical and isotopic signatures of synglaciogenic neoproterozoic banded iron formations bifs at bafq mining district bmd central iran the possible ediacaran missing link of bifs in tethyan metallogeny abstract the neoproterozoic magnetite apatite hematite pyrolusite jaspilite deposits in the bafq mining district bmd contain more than 1 7 gt ores with an average grade of 50 wt fe and 0 01 to 7 78 wt p and were probably formed between 635 and 547 ma in a riftogenic felsic submarine exhalative sequence of the esfordi formation the ore zones occur in proximal zone of magnetite rich albitized rhyolite keratophyres interdistal zone of rhyolitic tuff tuffaceous sediments and distal zone of pyrolusite jaspilite these sequences are covered by the diamictites and cap carbonates the bifs are linked to the altered rhyolites rhyodacites jaspilites and diamictites and contain magnetite hematite and apatite the presence of spriggina dickinsonia medusites and persimedusites chahgazensis sennewald and kruger 1979 hahn and pflug mccall 2006 in the kushk shale member of the esfordi formation conforms to the australian fauna of the ediacaran period 635 540 this relative age is supported by some reliable pb isotopic data 635 547 ma on galena monazite and apatite huckriede et al 1962 torab 2008 stosch et al 2011 the most frequent structures textures in the ore zones include felsic autobrecciation massive colloidal banded detrital and glaciogenic the bifs are highlighted by high values of lree fractionation and no significant eu and ce anomalies the ores show high values of fe 2 o 3 14 60 and sio 2 4 34 and low contents of al 3 32 cr 21 48 ppm co 42 82 ppm ni 125 ppm v 868 ppm and ti 0 13 similar to those of the ediacaran rapitan bifs the cap carbonates show depletion in 13 c with a range from 0 43 to 6 6 per mil and then return to near excursion of about 2 97 in the lower cambrian carbonates these are followed by 18 o values which range from 6 64 to 11 86 the presence of jaspilites diamictites c and o isotopic signatures ree patterns and immobile element relationships highlights a glaciogenic bif importantly the glaciogenic structures textures and jaspilites do not support the misconception of the previously proposed magmatic carbonatitic and metasomatic hydrothermal iocg kiruna ore deposits

the composition of the continental river weathering flux deduced from seawater mg isotopes this study establishes the magnesium isotopic composition of seawater and evaluates its constancy as a function of depth and geographic location it also provides results on the magnesium isotopic composition of river water samples draining specific lithologies in combination the results are used to obtain an average magnesium isotopic composition of 1 54 for the global continental weathering flux compared to the 2 value of the global ocean both relative to nist srm 980 analyses of modern and fossil carbonate secreting echinoderms suggest that these can serve as archives of seawater 26mg values it is demonstrated that these records of the magnesium isotopic composition of ancient oceans can be used to make important inferences about the relative contribution of different lithologies to the global continental weathering flux particularly carbonate versus silicate weathering preliminary results suggest that the composition of the continental weathering flux has not undergone dramatic changes during the phanerozoic

fluid inclusion and stable isotope study of the esfordi apatite magnetite deposit central iran a discussion sir we appreciate the effort and interesting contribution of jami et al 2007 on the origin of the esfordi apatite magnetite deposit we have been working in the bafq mining district of central iran for almost eight years resulting in three graduate theses on the mineralization of the area based on our field experiences and mineralogical and geochemical data we wish to comment on the conclusion of jami et al 2007 that esfordi is a typical kiruna type apatite magnetite deposit first the deposit is composed of magnetite apatite hematite rather than simply apatite magnetite and therefore does not fit an orthomagmatic model for fe mineralization furthermore many authors e g force et al 1991 consider kiruna type deposits as volcanic sedimentary complexes rather than as a simple although extended magmatic hydrothermal process such as proposed by jami 2005 and jami et al 2007 second the presence of actinolite albite chlorite and tourmaline in brecciated and altered rhyolite keratophyre is consistent with a submarine vent complex and feeder zone of an exhalative submarine volcanic system in this context the na metasomatism and albitic alteration could be due to interaction with seawater during submarine rhyolitic volcanism third there are many structural and textural features such as polymictic pebbly

coprecipitation and isotopic fractionation of boron in modern biogenic carbonates abstract the abundances and isotopic composition of boron in modern biogenic calcareous skeletons from the gulf of elat israel the great barrier reef australia and in deep sea sediments have been examined by negative thermal ionization mass spectrometry the selected species foraminifera pteropoda corals gastropoda and pelecypoda yield large variations in boron concentration that range from 1 ppm in gastropod shells to 80 ppm in corals the boron content of the biogenic skeletons is independent of mineralogical composition and is probably related to biological vital effects the 11 b values of the carbonates range from 14 2 to 32 2 relative to nbs srm 951 and overlap with the 11 b values of modern deep sea carbonate sediments 11 b 8 9 to 26 2 the variations of 11 b may be controlled by isotopic exchange of boron species in which 10 b is preferentially partitioned into the tetrahedral species and coprecipitation of different proportions of trigonal and tetrahedral species in the calcium carbonates carbonates with low 11 b values 15 may indicate preferential incorporation of tetrahedral species whereas the higher 11 b values 30 may indicate 1 1 uptake of both boron species assuming equilibrium with seawater 2 2 preferential incorporation of b oh 4 from in situ high ph internal fluids of organisms that are isolated from seawater the b content and 11 b values of deep sea sediments foraminifera tests and corals are used to estimate the global oceanic sink of elemental boron by calcium carbonate deposition as a result of enrichment of b in corals a substantially higher biogenic sink of 6 4 0 9 10 10 g yr is calculated for carbonates this is only slightly lower than the sink for desorbable b in marine sediments 10 10 10 g yr and approximately half that of altered oceanic crust 14 10 10 g yr thus carbonates are an important sink for b in the oceans being 20 of the total sinks the preferential incorporation of 10 b into calcium carbonate results in oceanic 11 b enrichment estimated as 1 2 0 3 10 12 per mil g yr the boron isotope composition of authigenic well preserved carbonate skeletons may provide a useful tool to record secular boron isotope variations in seawater at various times in the geological record the potential use of boron isotope geochemistry in skeletons as a tracer for palaeoenvironments is demonstrated in ostracoda and foraminifera from the gulf of carpentaria australia the 11 b values of glacial age buried skeletons 4 0 and 4 9 respectively are lower than that of their modern equivalents 17 6 and 13 3 respectively this may reflect a terrestrial boron isotope signature of the water in the gulf during the late quaternary when it was isolated from the ocean

response of central european sst to atmospheric pco2 forcing during the oligocene a combined proxy data and numerical climate model approach abstract co 2 induced global warming will affect seasonal to decadal temperature patterns expected changes will be particularly strong in extratropical regions where temperatures will increase at faster rates than at lower latitudes despite that it is still poorly constrained how precisely short term climate dynamics will change in a generally warmer world particularly in nearshore surface waters in the extratropics i e the ecologically most productive regions of the ocean on which many human societies depend specifically a detailed knowledge of the relationship between p co 2 and seasonal sst is crucial to understand interactions between the ocean and the atmosphere in the present investigation we have studied for the first time how rising atmospheric p co 2 levels forced surface temperature changes in central europe paleolatitude 45 n during the mid oligocene from ca 31 to 25 ma a time interval of earth history during which global conditions were comparable to those predicted for the next few centuries for this purpose we computed numerical climate models for the oligocene winter summer annual average assuming an atmospheric carbon dioxide rise from 400 to 560 ppm current level to two times pre industrial levels pal and from 400 to 840 ppm three times pal respectively these models were compared to seasonally resolved sea surface temperatures sst reconstructed from 18 o values of fossil bivalve shells glycymeris planicostalis g obovata palliolum pictum arctica islandica and isognomon maxillata sandbergeri and shark teeth carcharias cuspidata c acutissima and physogaleus latus collected from the shallow water deposits of the mainz and kassel basins germany multi taxon oxygen isotope based reconstructions suggest a gradual rise of temperatures in surface waters upper 30 to 40 m on average by as much as 4 c during the rupelian stage followed by a 4 c cooling during the chattian stage seasonal temperature amplitudes increased by ca 2 c during the warmest time interval of the rupelian stage with warming being more pronounced during summer 5 c than during winter 3 c according to numerical climate simulations the warming of surface waters during the early oligocene required a co 2 increase by at least 160 ppm i e 400 ppm to 560 ppm given that atmospheric carbon dioxide levels predicted for the near future will likely exceed this value significantly the early oligocene warming gives a hint of the possible future climate in central europe under elevated co 2 levels

the evolution of pco2 ice volume and climate during the middle miocene abstract the middle miocene climatic optimum 17 15 ma mco is a period of global warmth and relatively high co2 and is thought to be associated with a significant retreat of the antarctic ice sheet ais we present here a new planktic foraminiferal 11b record from 16 6 to 11 8 ma from two deep ocean sites currently in equilibrium with the atmosphere with respect to co2 these new data demonstrate that the evolution of global climate during the middle miocene as reflected by changes in the cyrosphere was well correlated to variations in the concentration of atmospheric co2 what is more within our sampling resolution 1 sample per 300 kyr there is no evidence of hysteresis in the response of ice volume to co2 forcing during the middle miocene contrary to what is understood about the antarctic ice sheet from ice sheet modelling studies in agreement with previous data we show that absolute levels of co2 during the mco were relatively modest 350 400 ppm and levels either side of the mco are similar or lower than the pre industrial 200 260 ppm these new data imply the presence of either a very dynamic ais at relatively low co2 during the middle miocene or the advance and retreat of significant northern hemisphere ice recent drilling on the antarctic margin and shore based studies indicate significant retreat and advance beyond the modern limits of the ais did occur during the middle miocene but the complete loss of the ais was unlikely consequently it seems that ice volume and climate variations during the middle miocene probably involved a more dynamic ais than the modern but also some component of land based ice in the northern hemisphere

iron oxide copper gold deposits an andean view iron oxide copper gold iocg deposits defined primarily by their elevated magnetite and or hematite contents constitute a broad ill defined clan related to a variety of tectono magmatic settings the youngest and therefore most readily understandable iocg belt is located in the coastal cordillera of northern chile and southern peru where it is part of a volcano plutonic arc of jurassic through early cretaceous age the arc is characterised by voluminous tholeiitic to calc alkaline plutonic complexes of gabbro through granodiorite composition and primitive mantle derived parentage major arc parallel fault systems developed in response to extension and transtension induced by subduction roll back at the retreating convergent margin the arc crust was attenuated and subjected to high heat flow iocg deposits share the arc with massive magnetite deposits the copper deficient end members of the iocg clan as well as with manto type copper and small porphyry copper deposits to create a distinctive metallogenic signature

boron isotopic composition of tourmaline prismatine and grandidierite from granulite facies paragneisses in the larsemann hills prydz bay east antarctica evidence for a non marine evaporite source a unique assemblage of b rich rocks 2 wt b containing the borosilicate minerals tourmaline tur prismatine prs and grandidierite gdd is exposed in the ca 1000 ma brattstrand paragneiss in the larsemann hills east antarctica the b isotope composition of these three minerals in 21 paragneisses and 6 anatectic pegmatites were measured in situ using secondary ion mass spectrometry 11b ranges from 2 8 to 14 4 in tourmaline from 9 6 to 17 8 in prismatine and from 2 8 to 8 7 in grandidierite weighted uncertainties mostly 1 2 per sample in most cases average 11b increases in a given sample prs tur gdd whether the observed b isotope distribution has attained equilibrium were assessed using two criteria microstructural equilibrium and regular distribution of mg and fe in samples for which the two criteria are met we assume the measured distribution of isotopes 11ba b 11ba 11bb represents equilibrium 11btur prs 5 0 1 4 5 of 12 pairs 11btur gdd 3 3 0 8 3 of 5 pairs and 11bgdd prs 7 2 1 3 2 of 2 pairs consistent with the preference of 10b for tetrahedral sites prismatine and 11b for trigonal sites tourmaline grandidierite ab initio computations of b isotope fractionation factors 11btur prs 6 4 1 3 11btur gdd 1 8 1 1 and 11bgdd prs 8 2 1 1 provide confirmation of the measured fractionations the computed relaxed ionic structure of grandidierite gave a shorter 1 368 a b o bond length than in case of dravite 1 385 a which explains the measured enrichment of grandidierite in 11b relative to tourmaline the precursor of the b rich rock least changed by metamorphism tourmaline metaquartzite 11b tur 8 6 to 5 9 is interpreted to be a product of pre metamorphic hydrothermal b metasomatism boron sources consistent with this 11b range include oceanic crust clastic sediments volcanic rocks and non marine evaporite borate but not marine evaporite however dominance of metasediments in the brattstrand paragneiss major and trace element compositions of the b rich rocks and presence of abundant b are consistent with non marine evaporite being the most important source of b for the b rich lithologies of the larsemann hills a possible scenario for precursors of these rocks is a succession of clastic sediments in part tuffaceous intercalated with b rich evaporite deposits in a continental rift basin in which circulating hydrothermal fluids leached b from the evaporite and precipitated it as tourmaline in the associated clastic rocks to form the precursors to the tourmaline metaquartzites

a core top assessment of proxies for the ocean carbonate system in surface dwelling foraminifers we have assessed the reliability of several foraminifer hosted proxies of the ocean carbonate system 11b b ca and u ca using holocene samples from the atlantic and pacific oceans we examined chemical variability over a range of test sizes for two surface dwelling foraminifers globigerinoides sacculifer and globigerinoides ruber measurements of 11b in g ruber show no significant relationship with test size in either atlantic or pacific sites and appear to provide a robust proxy of surface seawater ph likewise there is no significant variability in the 11b of our atlantic core top g sacculifer but we find that 11b increases with increasing test size for g sacculifer in the pacific these systematic differences in 11b are inferred to be a consequence of isotopically light gametogenic calcite in g sacculifer and its preferential preservation during postdepositional dissolution the trace element ratio proxies of ocean carbonate equilibria u ca and b ca show systematic increases in both g ruber and g sacculifer with increasing test size possibly as a result of changing growth rates this behavior complicates their use in paleoceanographic reconstructions in keeping with several previous studies we find that mg ca ratios increase with increasing size fraction in our well preserved atlantic g sacculifer but not in g ruber in contrast to previous interpretations we suggest that these observations reflect a proportionally larger influence of compositionally distinct gametogenic calcite in small individuals compared to larger ones as with 11b this influences g sacculifer but not g ruber which has negligible gametogenic calcite

experimental measurement of boron isotope fractionation in seawater abstract the boron isotopic composition of marine carbonates is considered to be a tracer of seawater ph use of this proxy benefits from an intimate understanding of chemical kinetics and thermodynamic isotope exchange reactions between the two dominant boron bearing species in seawater boric acid b oh 3 and borate ion b oh 4 however because of our inability to quantitatively separate these species in solution the degree of boron isotope exchange has only been known through theoretical estimates in this study we present results of a spectrophotometric procedure wherein the boron isotope equilibrium constant 11 10 k b is determined empirically from the difference in the dissociation constants of 11 b oh 3 and 10 b oh 3 in pure water 0 6 mol kg 1 h 2 o kcl and artificial seawater within experimental uncertainty our results show no dependence of 11 10 k b on temperature but 11 10 k b at 25 c in pure water was statistically different than results obtained in solutions at high ionic strength 11 10 k b of the seawater s 35 b t 0 01 mol kg 1 h 2 o at 25 c is 1 0272 0 0006 this result is significantly larger than the theoretical value used in numerous paleo ph studies 11 10 k b 1 0194

b ca in planktonic foraminifera as a proxy for surface seawater ph boron isotope systematics indicate that boron incorporation into foraminiferal caco3 is determined by the partition coefficient k d frac left rm b rm ca right rm caco3 left rm b left rm oh right 4 rm hco 3 right rm seawater and b oh 4 hco3 seawater providing in principle a method to estimate seawater ph and pco2 we have measured b ca ratios in globigerina bulloides and globorotalia inflata for a series of core tops from the north atlantic and the southern ocean and in globigerinoides ruber white from ocean drilling program odp site 668b on the sierra leone rise in the eastern equatorial atlantic b ca ratios in these species of planktonic foraminifera seem unaffected by dissolution on the seafloor k d shows a strong species specific dependence on calcification temperature which can be corrected for using the mg ca temperature proxy a preliminary study of g inflata from southern ocean sediment core chat 16k suggests that temperature corrected b ca was 30 higher during the last glacial correspondingly ph was 0 15 units higher and aqueous pco2 was 95 atm lower at this site at the last glacial maximum the covariation between reconstructed pco2 and the atmospheric pco2 from the vostok ice core demonstrates the feasibility of using b ca in planktonic foraminifera for reconstructing past variations in ph and pco2

history of carbonate ion concentration over the last 100 million years abstract instead of having been more or less constant as once assumed it is now apparent that the major ion chemistry of the oceans has varied substantially over time for instance independent lines of evidence suggest that calcium concentration ca2 has approximately halved and magnesium concentration mg2 approximately doubled over the last 100 million years on the other hand the calcite compensation depth and hence the caco3 saturation has varied little over the last 100 my as documented in deep sea sediments we combine these pieces of evidence to develop a proxy for seawater carbonate ion concentration co32 over this period of time from the calcite saturation state which is proportional to the product of ca2 times co32 but also affected by mg2 we can calculate seawater co32 our results show that co32 has nearly quadrupled since the cretaceous furthermore by combining our co32 proxy with other carbonate system proxies we provide calculations of the entire seawater carbonate system and atmospheric co2 based on this reconstructed atmospheric co2 is relatively low in the miocene but high in the eocene finally we make a strong case that seawater ph has increased over the last 100 my

boron isotopic compositions of corals seawater or diagenesis record abstract the first analyses of modern and fossil corals calcite free using a positive ion cs2bo2 tims technique and a chemical procedure for b extraction are reported the 11b for modern corals fluctuates between 23 3 and 25 5 the range of variation of fossil corals from the last interglacial period is greater from 23 5 to 27 3 and the lowest 11b corresponds to the corals close to last glacial maximum boron concentrations show a variation from 49 to 58 ppm in the recent corals and from 39 to 52 ppm in ancient corals for the ancient corals linear correlations are observed in both 11b vs b concentration and 11b vs 1 b plots but these correlations are not observed for modern corals two interpretations are presented to account for these observations and to test the potential of 11b for reconstructing paleo ocean ph the first interpretation assumes a thermodynamic partitioning of b between seawater and carbonates and shows that both boron isotopic compositions and concentrations can be used to calculate the ph of seawater in which corals grow for our data such a model requires that both the ph and the co2 of the deglacial ocean was lower than present day values the second interpretation is based on the correlation observed for ancient corals between boron isotopic compositions and 1 b we suggest that the measured boron isotopic compositions of ancient corals are caused by the mixing of a primary aragonite the coral skeleton and secondary aragonite precipitated from 10b enriched reef pore fluids the characteristics 11b and b concentrations of the diagenetic aragonite and the fluids from which it precipitates can be constrained if this proves correct only the non recrystallised parts of ancient corals can be used for paleo ph reconstructions these recrystallisation processes did not affect the 234u 238u ratios of the corals

changing atmospheric co2 concentration was the primary driver of early cenozoic climate the early eocene climate optimum eeco which occurred about 51 to 53 million years ago was the warmest interval of the past 65 million years with mean annual surface air temperature over ten degrees celsius warmer than during the pre industrial period subsequent global cooling in the middle and late eocene epoch especially at high latitudes eventually led to continental ice sheet development in antarctica in the early oligocene epoch about 33 6 million years ago however existing estimates place atmospheric carbon dioxide co2 levels during the eocene at 500 3 000 parts per million and in the absence of tighter constraints carbon climate interactions over this interval remain uncertain here we use recent analytical and methodological developments to generate a new high fidelity record of co2 concentrations using the boron isotope 11 b composition of well preserved planktonic foraminifera from the tanzania drilling project revising previous estimates although species level uncertainties make absolute values difficult to constrain co2 concentrations during the eeco were around 1 400 parts per million the relative decline in co2 concentration through the eocene is more robustly constrained at about fifty per cent with a further decline into the oligocene provided the latitudinal dependency of sea surface temperature change for a given climate forcing in the eocene was similar to that of the late quaternary period this co2 decline was sufficient to drive the well documented high and low latitude cooling that occurred through the eocene once the change in global temperature between the pre industrial period and the eocene caused by the action of all known slow feedbacks apart from those associated with the carbon cycle is removed both the eeco and the late eocene exhibit an equilibrium climate sensitivity relative to the pre industrial period of 2 1 to 4 6 degrees celsius per co2 doubling 66 per cent confidence which is similar to the canonical range 1 5 to 4 5 degrees celsius indicating that a large fraction of the warmth of the early eocene greenhouse was driven by increased co2 concentrations and that climate sensitivity was relatively constant throughout this period

nearshore along strike variability is the concept of the systems tract unhinged sequence stratigraphic models assume that nearshore strata have relatively consistent and laterally persistent stacking at the systems tract scale and therefore may not fully describe the three dimensional stratigraphic architecture in areas displaying marked nearshore along strike variability a stratigraphic model of nearshore deposits is presented that corrects for this assumption by explaining variations in along strike stratal geometries in terms of a systematic change in the orientation of a shoreline trend or clinoform rollover a scenario comparable to deflection around a hinge the model defines hinge zones that are both fixed and moving with respect to time and was created from outcrop well log and seismic reflection data model end members predict contemporaneous progradational aggradational and retrogradational stacking bounded by surfaces displaying significant along strike changes in architecture implying that sequence stratigraphic surfaces can be diachronous we advocate examining the impact of stratigraphic variations parallel to depositional strike by testing for the presence of uniform versus differential progradation phenomena responsible for creating unhinged and hinged nearshore depositional systems respectively understanding these differences will improve subsurface predictions and provide a more complete understanding of the stratigraphic evolution of sedimentary basins

precise magnesium isotope measurements in core top planktic and benthic foraminifera 1 this study presents a new methodology to obtain highly precise measurements 0 1 of magnesium isotope ratios in very small samples of foraminiferal carbonate 40 50 g here this technique is used to examine mg isotopic variation among different species of core top foraminifera over a range of different ambient conditions despite the high degree of temperature control on the abundance of elemental mg incorporated into foraminiferal tests analyses of surface dwelling globigerinoides ruber and g sacculifer from five cores with associated sea surface temperatures ranging from 20 to 31 c show no significant temperature dependent variations in their mg isotope ratios analyses of different size fractions of g sacculifer show an increase in mg ca with test size but no variation of mg isotope ratio in all nine planktic and benthic species were analyzed all show identical mg isotope ratios with a mean of 26mg 4 72 apart from small differences in three species namely o universa g sacculifer which are both 0 4 lighter than the average and p obliquiloculata which is 0 4 heavier these results highlight the constancy of foraminiferal mg isotope ratios despite changing environmental conditions which dominate mg ca variation and arguably affect ca isotope fractionation this is an important observation which needs to be included in any model of foraminiferal calcification the insusceptibility of 26mg values to external parameters makes mg isotopes ideally suited to constraining past variations in the mg isotope budget of the oceans and the information this carries about the history of oceanic dolomitization continental weathering and hydrothermal behavior

constraining the evolution of neogene ocean carbonate chemistry using the boron isotope ph proxy abstract over the course of the neogene the earth underwent profound climatic shifts from the sustained warmth of the middle miocene to the development of plio pleistocene glacial interglacial cycles major perturbations in the global carbon cycle have occurred alongside these shifts however the lack of long term carbonate system reconstructions currently limits our understanding of the link between changes in co2 carbon cycling and climate over this time interval here we reconstruct continuous surface ocean ph co2 and surface ocean aragonite saturation state using boron isotopes from the planktonic foraminifer trilobatus trilobus and we perform a sensitivity analysis of the key variables in our calculations e g 11 bsw ca sw ccd we show that the choice of 11 b sw influences both seawater ph and co2 while ca sw reconstructed dissolved inorganic carbon exerts a significant influence only on co2 over the last 22 myr the lowest ph levels occurred in the middle miocene climate optimum mmco 17 14 myr ago reaching 7 6 0 1 units in all our scenarios the extended warmth of the mmco corresponds to mean co2 and aragonite saturation state levels of 470 630 ppm and 2 7 3 5 respectively despite a general correspondence between our co2 record and climate all co2 scenarios show a peak at 9 ma not matched by corresponding changes in climate reconstructions this may suggest decoupling i e significant co2 change without a discernible climate response for a limited interval in the late miocene 11 6 8 5 ma although further refinement of our understanding of the temporal evolution of the boron isotopic composition of seawater is necessary to fully evaluate the nature of the relationship between co2 and climate nonetheless from our long term view it is clear that low latitude open ocean marine ecosystems are unlikely to have experienced sustained surface ph and saturation levels below 7 7 and 1 7 respectively during the past 14 million years 66 ci

cenozoic boron isotope variations in benthic foraminifers the boron isotopic composition of seawater 11 b sw is a prerequisite for reliably estimating past variation of seawater ph from boron isotopes in marine carbonates 11 b c here we compose a 50 m y stack of 11 b c from atlantic and pacific ocean deep sea sediments and discuss the potential effects of deep sea ph and 11 b sw on our record using model based cenozoic ph values the inferred 11 b sw values suggest an 3 increase since the late eocene superimposed on oscillating variations with amplitudes of up to 2 our estimates match existing reconstructions of 11 b sw but call into question published fluid 11 b in halite as a recorder of 11 b sw

mg isotopic composition of carbonate insight from speleothem formation simultaneous high precision measurement of 24 mg 25 mg and 26 mg isotopic compositions were made by multiple collector inductively coupled mass spectrometry mc icp ms relative to the international standard srm980 data are presented on low mg calcite speleothems and their associated host rocks and waters from four caves one in the french alps and three in israel covering various climate conditions in addition data are presented on three dolostones and three limestones from the himalaya the overall variation is 4 13x and 2 14x in n 26 mg and n 25 mg respectively this is 35 times the uncertainty of the measurements and clearly demonstrates that the terrestrial isotopic composition of mg is not unique each speleothem shows a characteristic range of n 26 mg values that are attributed to the isotopic composition of the local water differences between the isotopic composition of mg in the water dripping from stalactites and that of the modern speleothem are interpreted as being due to mg isotopic fractionation during carbonate precipitation in the temperature range of 4 18 c the low mg calcite is enriched in light isotopes by 1 35x amu and the dependence on temperature has been found to be less than 0 02x amu c despite various geological settings the n 26 mg of the studied dolostones is 2 0 1 2x higher than the n 26 mg of the limestones all together these results suggest a strong mineralogical control and a weak temperature effect on the mg isotopic composition of carbonate a 2002 elsevier science b v all rights reserved

geological evolution of seawater boron isotopic composition recorded in evaporites the abundance of boron isotopes in ancient marine carbonates can be used to estimate oceanic ph that reflects atmospheric co 2 levels this proxy requires that the boron isotopic composition of seawater at the time the carbonate has formed is known and thus the past changes in seawater chemistry here we report the boron isotopic composition of selected ancient marine halites and modern sea salts the signal interpreted as marine reveals a clear evolution of the boron isotopic composition of seawater to 8 variations over the cenozoic comparison between this reconstructed curve and the mg ca ratio reveals a high level of consistency that will help to better define oceanic geochemical cycles

convergent cenozoic co2 history reconstructions of atmospheric carbon dioxide concentrations over the past 65 million years are heading towards consensus it is time for systematic testing of the proxies against measurements and against each other

plio pleistocene climate sensitivity evaluated using high resolution co2 records theory and climate modelling suggest that the sensitivity of earth s climate to changes in radiative forcing could depend on the background climate however palaeoclimate data have thus far been insufficient to provide a conclusive test of this prediction here we present atmospheric carbon dioxide co2 reconstructions based on multi site boron isotope records from the late pliocene epoch 3 3 to 2 3 million years ago we find that earth s climate sensitivity to co2 based radiative forcing earth system sensitivity was half as strong during the warm pliocene as during the cold late pleistocene epoch 0 8 to 0 01 million years ago we attribute this difference to the radiative impacts of continental ice volume changes the ice albedo feedback during the late pleistocene because equilibrium climate sensitivity is identical for the two intervals when we account for such impacts using sea level reconstructions we conclude that on a global scale no unexpected climate feedbacks operated during the warm pliocene and that predictions of equilibrium climate sensitivity excluding long term ice albedo feedbacks for our pliocene like future with co2 levels up to maximum pliocene levels of 450 parts per million are well described by the currently accepted range of an increase of 1 5 k to 4 5 k per doubling of co2

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

reply to discussion by sadegh mohseni and alijan aftabi of significance of apatite ree depletion and monazite inclusions in the brecciated se chahun iron oxide apatite deposit bafq district iran insights from paragenesis and geochemistry by bonyadi z davidson g j mehrabi b meffre s ghazban f chemical geology 281 2011 253 269

apatite monazite relations in the kiirunavaara magnetite apatite ore northern sweden the magnetite apatite ores in the kiruna area northern sweden are generally considered to be of magmatic origin formed in a subvolcanic volcanic environment during the early proterozoic they are thought to have crystallised from volatile rich iron oxide magmas derived by immiscibility in calc alkaline to slightly alkaline parental magmas three major morphological types of the magnetite apatite ore primary brecciated and banded have been investigated for textural relations and mineral chemistry using transmitted light back scattered electron imaging bse electron microprobe analysis empa and laser ablation inductively coupled plasma mass spectrometry la icpms in all three types th and u poor monazite is present as small inclusions in the apatite larger up to 150 m recrystallised monazite grains both along apatite grain boundaries and intergrown with magnetite and silicate minerals are present in the brecciated and banded samples primary apatite grains without monazite inclusions are generally enriched in light rare earth elements lrees together with na and si petrological and mineralogical evidence suggest that the kiruna magnetite apatite ore experienced successive stages of fluid rock interaction the first stage occurred under high temperature conditions 700 800 c shortly after emplacement and crystallisation of the ore magmas and involved concentrated probably cl dominated brines expelled from the magma this fluid is held to be responsible for the nucleation of the numerous small monazite inclusions within the apatite due to high temperature leaching of na and si while the lrees were concentrated in the monazite the large monazite grains in the brecciated and banded samples are proposed to be the product of recrystallisation from the much smaller monazite inclusions during greenschist facies metamorphism t 300 400 c fluids from the surrounding country rock caused strong lree na si depletion along apatite grain boundaries and cracks in the apatite lrees were either redeposited as monazite grains along apatite grain boundaries or were flushed out of the ore this fluid interaction also introduced the silicate components responsible for the interstitial formation of allanite talc tremolite chlorite serpentine muscovite quartz and carbonates along apatite grain boundaries

surface ocean ph response to variations in pco2 through two full glacial cycles abstract knowledge of past atmospheric pco 2 is important for evaluating the role of greenhouse gases in climate forcing ice core records show the tight correlation between climate change and pco 2 but records are limited to the past 900 kyr we present surface ocean ph and pco 2 data reconstructed from boron isotopes in planktonic foraminifera over two full glacial cycles 0 140 and 300 420 kyr the data co vary strongly with the vostok pco 2 record and demonstrate that the coupling between surface ocean chemistry and the atmosphere is recorded in marine archives allowing for quantitative estimation of atmospheric pco 2 beyond the reach of ice cores

thick turbidite successions from supply dominated shelves during sea level highstand emphasis on the association between relative sea level lowstand and the formation of sandy deep water fans has tended to downplay the significance of high sediment supply and its potential to create deep water fans even during sea level highstands the lance fox hills lewis shelf margin in southern wyoming suggests that high supply was critical in causing the accretion of this moderately wide maastrichtian shelf margin at a minimum rate of 47 8 km m y and the generation of large sand rich fans during every shoreline regression across the shelf it is surprising that fans developed from shelf margin clinoforms that show systematically rising shelf edge trajectories proxy for rising relative sea level as well as from those that show flat trajectories stable to falling relative sea level however the latter producing more sediment bypass resulted in bigger and thicker fans whereas the former produced somewhat smaller and thinner fans we term the former highstand fans and suggest caution in using the lowstand model for high supply systems

ground truthing the boron isotope paleo ph proxy in planktonic foraminifera shells partial dissolution and shell size effects 1 sediment samples from the ontong java plateau in the pacific and the 90 east ridge in the indian ocean were used to investigate whether shell size and early diagenesis affect 11b of the symbiont bearing planktonic foraminifer globigerinoides sacculifer in pristine shells from both study locations we found a systematic increase of 11b and mg ca with shell size shells in the sieve size class 515 865 m revealed 11b values 2 1 to 2 3 higher than shells in the 250 380 m class this pattern is most likely due to differences in symbiont photosynthetic activity and its integrated effect on the ph of the foraminiferal microenvironment we therefore suggest smaller individuals must live at approximately 50 100 m water depth where ambient light levels are lower using the empirical calibration curve for 11b in g sacculifer only shells larger than 425 m reflect surface seawater ph partial dissolution of shells derived from deeper sediment cores was determined by shell weight analyses and investigation of the shell surface microstructure by scanning electron microscopy the 11b in partially dissolved shells is up to 2 lower relative to pristine shells of the same size class in agreement with a relatively higher weight loss in smaller shells samples from the ontong java plateau show a more pronounced dissolution effect than larger shells on the basis of the primary size effect and potential postdepositional dissolution effects we recommend the use of shells that are visually pristine and in the case of g sacculifer larger than 500 m for paleoreconstructions