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

the intensification of northern component deepwater formation during the mid pleistocene climate transition we reconstruct mid pleistocene marine isotope stages miss 13 18 deepwater hydrography at ocean drilling program site 1063 4583 m water depth subtropical north atlantic using benthic foraminiferal stable isotope records these new records complete an 900 kyr long stratigraphy spanning miss 8 29 250 1030 ka when combined with previously published records from site 1063 the results indicate a change in the circulation regime of the abyssal subtropical north atlantic during mis 17 prior to mis 17 no significant glacial or interglacial 13c gradients are evident between site 1063 and the deep south atlantic after mis 17 interglacial intervals at site 1063 are characterized by 13c values that consistently approach those recorded in the deep north atlantic comparing site 1063 13c values to 26 additional published records throughout the entire atlantic basin supports the idea that this 13c increase is unique to the deep north atlantic after mis 17 the basin wide influence of higher 13c values suggests an increased relative flux of northern sourced bottom waters during interglacial periods the timing of northern sourced water influence at site 1063 is consistent with the timing of a shift in the orientation of the arctic front thus this shift may signify a link between the northward penetration of relatively warm saline surface waters into the norwegian greenland seas stimulating deep convection our findings fit well with the model of imbrie et al 1993 for the importance of the nordic heat pump in establishing strong 100 kyr cyclicity in late pleistocene glacial cycles

a new method for calibrating a boron isotope paleo ph proxy using massive porites corals the boron isotope ratio 11b of marine biogenic carbonates can reconstruct ph and pco2 of seawater and potentially co2 concentration in the atmosphere to date 11b phsw calibration has been proposed via culturing experiments where calcifying organisms are cultured under artificially acidified seawater however in scleractinian corals reconstructed ph values using culture based calibrations do not agree well with actual observations of seawater co2 chemistry thus another approach is needed to establish a more reliable calibration method in this study we established field based calibrations for chichijima and tahiti both located in subtropical gyres where surface seawater is close to co2 equilibrium we suggest a new approach to calibration of 11b ph in which the long term 11b variation of massive porites corals is compared with the decreasing ph trend i e ocean acidification that has occurred since the industrial revolution this calibration will offer a new avenue for studying seawater co2 chemistry using coral 11b in diverse settings such as upwelling regions coral reefs and coastal areas

co2 over the past 5 million years continuous simulation and new δ11b based proxy data during the past five million yrs benthic 18o records indicate a large range of climates from warmer than today during the pliocene warm period to considerably colder during glacials antarctic ice cores have revealed pleistocene glacial interglacial co2 variability of 60 100 ppm while sea level fluctuations of typically 125 m are documented by proxy data however in the pre ice core period co2 and sea level proxy data are scarce and there is disagreement between different proxies and different records of the same proxy this hampers comprehensive understanding of the long term relations between co2 sea level and climate here we drive a coupled climate ice sheet model over the past five million years inversely forced by a stacked benthic 18o record we obtain continuous simulations of benthic 18o sea level and co2 that are mutually consistent our model shows co2 concentrations of 300 to 470 ppm during the early pliocene furthermore we simulate strong co2 variability during the pliocene and early pleistocene these features are broadly supported by existing and new 11b based proxy co2 data but less by alkenone based records the simulated concentrations and variations therein are larger than expected from global mean temperature changes our findings thus suggest a smaller earth system sensitivity than previously thought this is explained by a more restricted role of land ice variability in the pliocene the largest uncertainty in our simulation arises from the mass balance formulation of east antarctica which governs the variability in sea level but only modestly affects the modeled co2 concentrations

modern and late pleistocene b ca ratios of the benthic foraminifer planulina wuellerstorfi determined with laser ablation icp ms incorporation of boron into foraminiferal shells is thought to be primarily governed by the carbonate chemistry of the ambient seawater suggesting that it can be reconstructed from b ca ratios to this end b ca ratios of the benthic foraminifer planulina wuellerstorfi from south atlantic core top samples have been analyzed using laser ablation inductively coupled plasma mass spectroscopy la icp ms to provide additional information on intratest trace element heterogeneity results show that boron is heterogeneously distributed within and between shells with content variations of approximately 43 displayed within a single shell b ca is higher in the youngest chambers opposite to the observed between chamber variability of mg ca this may be explained by ontogenetic changes of physiological processes that increase the ph of the calcifying fluid and thus the borate concentration while decreasing mg ca to promote calcification despite this heterogeneity mean b ca ratios are positively correlated with the deepwater calcite saturation state co32 in line with previous studies we apply this empirical relationship to reconstruct co32 for the late pleistocene to holocene using samples from a depth transect in the equatorial atlantic reconstructed co32 values confirm previous studies suggesting that caco3 oversaturated north atlantic deep water was reduced during glacial periods whereas caco3 undersaturated antarctic bottom water expanded vertically and propagated northwards in summary our data demonstrate that bulk b ca in p wuellerstorfi reliably reflects variations in co32 despite the strong physiological control of boron incorporation

empirical relationship between ph and the boron isotopic composition of globigerinoides sacculifer implications for the boron isotope paleo ph proxy culture experiments were carried out with the planktonic foraminifera globigerinoides sacculifer at three different ph values 7 6 0 05 8 20 0 05 8 60 0 05 in order to establish the ph dependence of the boron isotopic fractionation between the calcitic tests of g sacculifer and seawater additional objectives were to compare the ph dependences of boron isotopic composition of g sacculifer with that of orbulina universa and inorganic calcite in order to evaluate the robustness of the boron isotope paleo ph proxy the relationship between the boron isotopic composition of g sacculifer and the culture water ph shows heavier boron isotopic values at higher ph this empirical relationship is similar but slightly offset by 3 per mil from that of o universa indicating the presence of biogenic influence vital effect on the boron isotopic composition of foraminifera however comparison of the boron isotopic composition of o universa and g sacculifer with that of inorganic calcite grown over a common ph range shows that inorganic processes are the dominant control on the boron isotopic composition of foraminifera and the vital effects play a small but not insignificant role the results imply that in spite of a small biogenic influence the variation in boron isotopic composition of foraminiferal shells with ph at least for o universa and g sacculifer is consistent with that for inorganic calcite demonstrating the potential of this isotopic signature in foraminifera as a reliable paleo ph proxy

refining the alkenone pco2 method i lessons from the quaternary glacial cycles abstract the alkenone pco2 method is one of the most widely used approaches to reconstruct atmospheric co2 in the cenozoic the method depends upon fractionation of stable carbon isotopes during algal photosynthesis expressed as ep37 2 and a physiological scaling parameter b that accounts for biological factors such as growth rate cell size and membrane permeability alkenone derived co2 records for the late pleistocene however are poorly correlated with ice core co2 challenging the classic model that considers most of the co2 used for coccolithophore photosynthesis to be acquired through simple diffusion in this study we investigate the nature of the b term and the underlying patterns of the sensitivity of ep37 2 to pco2 changes we generated two new ep37 2 records from the south china sea md01 2392 and tropical atlantic ocean odp 668b and compiled other published ep37 2 records over glacial interglacial cycles using the ep37 2 data ocean temperature estimates and ice core co2 we were able to back calculate the corresponding values of b at all locations b varies over glacial cycles the highest values of b correspond to peak interglacial stages indicating that the phytoplankton growth rate is faster or cell size is smaller during interglacials than during glacial periods we further show that the range of ep37 2 between glacial and interglacial conditions ep37 2 scales with growth conditions consistent with the predictions of the carbon isotope fractionation model based on co2 diffusion in other words the sensitivity of ep37 2 to pco2 changes increases where the modern b values are large contradicting the recommendations that oligotrophic sites are the best for alkenone co2 applications because of the presumed stability of b using the average back calculated b value for each site the composite pco2 estimates from md01 2392 and odp 668b the two sites with adequate ep37 2 sensitivity show broad agreement with the ice core co2 record

late pliocene pleistocene environments and glacial history of the northern north sea abstract based on new geochronological amino acids and sr isotopes and lithological data combined with analyses of 3d seismic data the pliocene pleistocene development of the central northern north sea has been investigated at the start of the plio pleistocene transition the study area was dominated by a deltaic shallow marine or tidal depositional environment with sediments mainly sourced from the west these sand rich sediments include green glauconitic grains that belong to the utsira sand with a local provenance directly above the base quaternary r2 a 60 m thick layer of mud rich sediments of glacimarine origin were deposited at a rate of 12 cm ka between 2 1 5 ma and up to 80 cm ka between 1 5 and 1 2 ma possibly reflecting glacial ice advancing to the norwegian coastline the high rate of deposition in the early pleistocene occurred immediately before the initiation of the norwegian channel ice stream at 1 1 ma following this a large part of the sediment input from fennoscandia seems to have been directed away from the study area to the shelf break at the start of the mid pleistocene transition mpt subaerial conditions allowed the formation of a 50 km long fluvial channel across the study area draining water from the east to the south west the earliest evidence of grounded ice in the investigated area comes from mega scale glacial lineations formed during the mpt at or just after 1 2 ma following this a regional unconformity r4 was formed by one or more grounded ice advances across the study area possibly during or directly after the mpt and likely marks the boundary between the early and mid pleistocene glacimarine sediments the mid to late pleistocene stratigraphy is dominated by glacimarine sediments and tills and is associated with multiple generations of tunnel valleys observed within the seismic data a high shear strength till containing chalk clasts transported from the west and or south of the study area was likely deposited during mis6 and may have been more conducive to tunnel valley formation in comparison to lower shear strength tills deposited by later ice advances a thick till unit overlain by a sand layer in the study area was deposited by grounded ice during the last glacial maximum and subsequent drainage of an ice dammed lake in the southern north sea during the last deglaciation mis2 of the study area this study shows that much of the quaternary age sediments within the northern north sea were deposited relatively rapidly during short periods of time probably leaving significant hiatuses within the stratigraphic record this finding has implications for previous studies that use a chronological framework assuming a relatively continuous sedimentation rate and record for the early pleistocene within the north sea

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

links between iron supply marine productivity sea surface temperature and co2 over the last 1 1 ma received 3 july 2008 revised 9 october 2008 accepted 27 october 2008 published 14 february 2009 1 paleoclimatic reconstructions have provided a unique data set to test the sensitivity of climate system to changes in atmospheric co2 concentrations however the mechanisms behind glacial interglacial g ig variations in atmospheric co2 concentrations observed in the antarctic ice cores are still not fully understood here we present a new multiproxy data set of sea surface temperatures sst dust and iron supply and marine export productivity from the marine sediment core ps2489 2 odp site 1090 located in the subantarctic atlantic that allow us to evaluate various hypotheses on the role of the southern ocean so in modulating atmospheric co2 concentrations back to 1 1 ma we show that antarctic atmospheric temperatures are closely linked to changes in so surface temperatures over the last 800 ka and use this to synchronize the timescales of our marine and the european project for ice coring in antarctica epica dome c edc records the close correlation observed between iron inputs and marine export production over the entire interval implies that the process of iron fertilization of marine biota has been a recurrent process operating in the subantarctic region over the g ig cycles of the last 1 1 ma however our data suggest that marine productivity can only explain a fraction of atmospheric co2 changes up to around 40 50 ppmv occurring at glacial maxima in each glacial stage in this sense the good correlation of our sst record to the edc temperature reconstruction suggests that the initial glacial co2 decrease as well as the change in the amplitude of the co2 cycles observed around 400 ka was most likely driven by physical processes possibly related to changes in antarctic sea ice extent surface water stratification and westerly winds position

obliquity and precession as pacemakers of pleistocene deglaciations abstract the milankovitch theory states that the orbital eccentricity precession and obliquity of the earth influence our climate by modulating the summer insolation at high latitudes in the northern hemisphere despite considerable success of this theory in explaining climate change over the pleistocene epoch 2 6 0 01 myr ago it is inconclusive with regard to which combination of orbital elements paced the 100 kyr glacial interglacial cycles over the late pleistocene here we explore the role of the orbital elements in pacing the pleistocene deglaciations by modeling ice volume variations in a bayesian approach when comparing models this approach takes into account the uncertainties in the data as well as the different degrees of model complexity we find that the earth s obliquity axial tilt plays a dominant role in pacing the glacial cycles over the whole pleistocene while precession only becomes important in pacing major deglaciations after the transition of the dominant period from 41 kyr to 100 kyr the mid pleistocene transition we also find that geomagnetic field and orbital inclination variations are unlikely to have paced the pleistocene deglaciations we estimate that the mid pleistocene transition took place over a 220 kyr interval centered on a time 715 kyr ago although the data permit a range of 600 1000 kyr this transition occurring within just two 100 kyr cycles indicates a relatively rapid change in the climate response to insolation

assessing ocean alkalinity for carbon sequestration over the coming century humanity may need to find reservoirs to store several trillions of tons of carbon dioxide co2 emitted from fossil fuel combustion which would otherwise cause dangerous climate change if it were left in the atmosphere carbon storage in the ocean as bicarbonate ions by increasing ocean alkalinity has received very little attention yet recent work suggests sufficient capacity to sequester copious quantities of co2 it may be possible to sequester hundreds of billions to trillions of tonnes of c without surpassing post industrial average carbonate saturation states in the surface ocean when globally distributed the impact of elevated alkalinity is potentially small and may help ameliorate the effects of ocean acidification however the local impact around addition sites may be more acute but is specific to the mineral and technology the alkalinity of the ocean increases naturally because of rock weathering in which 1 5 moles of carbon are removed from the atmosphere for every mole of magnesium or calcium dissolved from silicate minerals e g wollastonite olivine anorthite and 0 5 moles for carbonate minerals e g calcite dolomite these processes are responsible for naturally sequestering 0 5 billion of co2 tons per year alkalinity is reduced in the ocean through carbonate mineral precipitation which is almost exclusively formed from biological activity most of the previous work on the biological response to changes in carbonate chemistry have focused on acidifying conditions more research is required to understand carbonate precipitation at elevated alkalinity to constrain the longevity of carbon storage a range of technologies have been proposed to increase ocean alkalinity accelerated weathering of limestone enhanced weathering electrochemical promoted weathering ocean liming the cost of which may be comparable to alternative carbon sequestration proposals e g 20 100 tco2 1 there are still many unanswered technical environmental social and ethical questions but the scale of the carbon sequestration challenge warrants research to address these

boron isotope based seasonal paleo ph reconstruction for the southeast atlantic a multispecies approach using habitat preference of planktonic foraminifera abstract the boron isotopic composition of planktonic foraminiferal shell calcite 11 b cc provides valuable information on the ph of ambient water at the time of calcification hence 11 b cc of fossil surface dwelling planktonic foraminifera can be used to reconstruct ancient aqueous p co 2 if information on a second carbonate system parameter temperature and salinity is available however ph and p co 2 of surface waters may vary seasonally largely due to changes in temperature dic and alkalinity as also the shell fluxes of planktonic foraminifera show species specific seasonal patterns that are linked to intra annual changes in temperature it is obvious that 11 b cc of a certain species reflects the ph and thus p co 2 biased towards a specific time period within a year this is important to consider for the interpretation of fossil 11 b cc records that may mirror seasonal ph signals here we present new multi collector inductively coupled mass spectrometry mc icpms 11 b cc coretop data for the planktonic foraminifera species globigerina bulloides globigerinoides ruber trilobatus sacculifer and orbulina universa and compare them with 11 b borate derived from seasonally resolved carbonate system parameters we show that the inferred season adjusted 11 b cc 11 b borate relationships are similar to existing calibrations and can be combined with published 11 b cc field and culture data to augment paleo ph calibrations to test the applicability of these calibrations we used a core drilled on the walvis ridge in the southeast atlantic spanning the last 330 000 years to reconstruct changes in surface water p co 2 the reconstruction based on g bulloides which reflects the austral spring season was shown to yield values that closely resemble the vostok ice core data indicating that surface water p co 2 was close to equilibrium with the atmosphere during the cooler spring season in contrast p co 2 estimated from 11 b cc of o universa t sacculifer and g ruber that predominantly lived during the warmer seasons exhibits up to 50 ppmv higher values than the vostok ice core data this is probably due to the higher austral summer and fall temperatures as shown by mg ca to be on average 4 c higher than during the cooler spring season accounting for an increase in p co 2 of 4 per 1 c our results demonstrate that paleo ph estimates based on 11 b cc contain a significant seasonal signal reflecting the habitat preference of the recording foraminifera species

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

evaluation of boron isotope ratio as a ph proxy in the deep sea coral desmophyllum dianthus evidence of physiological ph adjustment the boron isotope ratio 11b of foraminifers and tropical corals has been proposed to record seawater ph to test the veracity and practicality of this potential paleo ph proxy in deep sea corals samples of skeletal material from twelve archived modern desmophyllum dianthus d dianthus corals from a depth range of 274 1470 m in the atlantic pacific and southern oceans ambient ph range 7 57 8 05 were analyzed for 11b the 11b values for these corals spanning a range from 23 56 to 27 88 are found to be related to seawater borate 11b by the linear regression 11bcoral 0 76 0 28 11bborate 14 67 4 19 1 standard error se the d dianthus 11b values are greater than those measured in tropical corals and suggest substantial physiological modification of ph in the calcifying space by a value that is an inverse function of seawater ph this mechanism partially compensates for the range of ocean ph and aragonite saturation at which this species grows enhancing aragonite precipitation and suggesting an adaptation mechanism to low ph environments in intermediate and deep waters consistent with the findings of trotter et al 2011 for tropical surface corals the data suggest an inverse correlation between the magnitude of a biologically driven ph offset recorded in the coral skeleton and the seawater ph described by the equation ph ph recorded by coral seawater ph 0 75 0 12 phw 6 88 0 93 1 se error analysis based on 95 confidence interval ci and the standard deviation of the regression residuals suggests that the uncertainty of seawater ph reconstructed from 11bcoral is 0 07 to 0 12 ph units this study demonstrates the applicability of 11b in d dianthus to record ambient seawater ph and holds promise for reconstructing oceanic ph distribution and history using fossil corals

evolution of the eastern tropical pacific through plio pleistocene glaciation a tropical pacific climate state resembling that of a permanent el nino is hypothesized to have ended as a result of a reorganization of the ocean heat budget 3 million years ago a time when large ice sheets appeared in the high latitudes of the northern hemisphere we report a high resolution alkenone reconstruction of conditions in the heart of the eastern equatorial pacific eep cold tongue that reflects the combined influences of changes in the equatorial thermocline the properties of the thermocline s source waters atmospheric greenhouse gas content and orbital variations on sea surface temperature sst and biological productivity over the past 5 million years our data indicate that the intensification of northern hemisphere glaciation 3 million years ago did not interrupt an almost monotonic cooling of the eep during the plio pleistocene sst and productivity in the eastern tropical pacific varied in phase with global ice volume changes at a dominant 41 000 year obliquity frequency throughout this time changes in the southern hemisphere most likely modulated most of the changes observed

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

climate transition in the asia inland at 0 8 0 6 ma related to astronomically forced ice sheet expansion abstract knowing the evolution history of the climate systems in the asian inland dominated by either the westerlies or the asian monsoon and understanding their associated driving mechanisms are crucial for assessing future trends of climate and environmental conditions in this region but both the evolution and mechanisms are still under debate in this study we present a comparative analysis of massive data from an accurately dated drill core retrieved from the westerlies controlled western qaidam basin qb with records from the chinese loess plateau clp dominated by the east asia summer monsoon easm to track the time and frequency domain evolution patterns and dynamic changes of the qb and the clp systems the results infer two main conclusions first a critical transition in the evolution of qaidam paleolake occurred at 0 8 0 6 ma characterized by striking changes in proxy variations and a system shift from periodic variations to more irregular fluctuations after 0 6 ma second a similar evolution pattern prevailed in the qaidam paleolake region and in the easm dominated clp between 2 7 and 1 2 ma but a divergence of both systems started at 1 2 ma and fully established after 0 6 ma when largely fluctuating climate conditions in the qb with a distinct drying trend was accompanied by synchronous largely fluctuated easm with an increasing trend after 0 6 ma we suggest that ice sheet expansion in the northern hemisphere promoted by co occurrence of low obliquity amplitudes and low eccentricity drove both systems across a threshold at 1 2 ma and the internal forcing due to glaciation disturbed the previous response of both systems to solar insolation and led to the divergence of two systems at 0 9 0 8 ma a node of the 1 2 myr obliquity cycle co occurred with an eccentricity minimum which together with coeval decrease in atmospheric co2 concentration could have facilitated a striking expansion of ice sheets the resulting more equatorial and zonally oriented northern hemisphere westerly jet could serve as key factor leading to the final collapse of qaidam paleolake after 0 6 ma and the divergence of the qb and the clp systems

the middle pleistocene transition characteristics mechanisms and implications for long term changes in atmospheric pco2 abstract the emergence of low frequency high amplitude quasi periodic 100 kyr glacial variability during the middle pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system this middle pleistocene transition mpt began 1250 ka and was complete by 700 ka its onset was accompanied by decreases in sea surface temperatures ssts in the north atlantic and tropical ocean upwelling regions and by an increase in african and asian aridity and monsoonal intensity during the mpt long term average ice volume gradually increased by 50 m sea level equivalent whereas low frequency ice volume variability experienced a 100 kyr lull centered on 1000 ka followed by its reappearance 900 ka although as a broad band of power rather than a narrow persistent 100 kyr cycle additional changes at 900 ka indicate this to be an important time during the mpt beginning with an 80 kyr event of extreme sst cooling followed by the partial recovery and subsequent stabilization of long term north atlantic and tropical ocean ssts increasing southern ocean sst variability primarily associated with warmer interglacials the loss of permanent subpolar sea ice cover and the emergence of low frequency variability in pacific ssts and global deep ocean circulation since 900 ka ice sheets have been the only component of the climate system to exhibit consistent low frequency variability with the exception of a near universal organization of low frequency power associated with marine isotope stages 11 and 12 all other components show an inconsistent distribution of power in frequency time space suggesting a highly nonlinear system response to orbital and ice sheet forcing most hypotheses for the origin of the mpt invoke a response to a long term cooling possibly induced by decreasing atmospheric pco2 none of these hypotheses however accounts for the geological constraint that the earliest northern hemisphere ice sheets covered a similar or larger area than those that followed the mpt given that the mpt was associated with an increase in ice volume this constraint requires that post mpt ice sheets were substantially thicker than pre mpt ice sheets indicating a change in subglacial conditions that influence ice dynamics we review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline precambrian shield bedrock became exposed by glacial erosion of a thick mantle of regolith this exposure of a high friction substrate caused thicker ice sheets with an attendant change in their response to the orbital forcing marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the mpt if this carbon came from terrigenous sources an increase in atmospheric pco2 would be likely which is inconsistent with evidence for widespread cooling apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith a more likely source of organic carbon and nutrients which would mitigate pco2 rise is from shelf and upper slope marine sediments which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the mpt modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long term silicate weathering rates in good agreement with marine sr and os isotopic records we use a carbon cycle model to show that a post mpt increase in silicate weathering rates would lower atmospheric pco2 by 7 12 ppm suggesting that the attendant cooling may have been an important feedback in causing the mpt

the mid pleistocene transition in the tropical pacific a sea surface temperature sst record based on planktonic foraminiferal magnesium calcium ratios from a site in the western equatorial pacific warm pool reveals that glacial interglacial oscillations in sst shifted from a period of 41 000 to 100 000 years at the mid pleistocene transition 950 000 years before the present sst changes at both periodicities were synchronous with eastern pacific cold tongue ssts but preceded changes in continental ice volume the timing and nature of tropical pacific sst changes over the mid pleistocene transition implicate a shift in the periodicity of radiative forcing by atmospheric carbon dioxide as the cause of the switch in climate periodicities at this time

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

remobilization of surficial slope sediment triggered by the a d 2011 mw 9 tohoku oki earthquake and tsunami along the japan trench the a d 2011 tohoku oki m w 9 earthquake ruptured the megathrust up to the japan trench with a large displacement and caused a catastrophic tsunami this study is the first to use short lived radioisotopes including those emitted by the damaged nuclear reactors at the fukushima daiichi nuclear power plant japan to document the remobilization of the upper few centimeters of sediment as a highly significant process triggered by the earthquake and its aftershocks targeting the post earthquake environment allowed characterization of the sedimentary signature of this event for a better understanding of paleoearthquakes in japan and other tectonically active boundary areas the results stem from 23 piston cores recovered by the 2013 expedition nt13 19 of the japan agency for marine earth science and technology we document submarine homogeneous muddy flow deposits that were triggered by ground motion in 2011 they are highly enriched with excess xs xs 210 pb requiring only centimeters deep sediment remobilization over large areas of the seafloor some contain 134 cs and 137 cs radioisotopes derived from the fukushima nuclear reactors indicating that sedimentation persisted for at least 30 days after the main shock we found these deposits at all sampling sites in an 5000 km 2 area of the seafloor in 4000 6000 m of water depth the study area extends for 260 km parallel to the strike of the trench the thickness of this tohoku layer 3 200 cm increases toward the zone of maximum megathrust slip where deposits are thickest these results demonstrate that the shaking of the seafloor above large megathrust ruptures near the trench remobilized surficial unconsolidated sediment for hundreds of kilometers the characteristics of these deposits may typify deposits resulting from large fault slips like that of the tohoku oki earthquake but also other earthquake deposits contributing to their identification in the sedimentary record globally

impacts of ph and co32 on the incorporation of zn in foraminiferal calcite the trace elemental composition of foraminiferal shell calcite is known to reflect the environment in which the shell was precipitated whereas conservative elements incorporated in foraminiferal shell carbonate reflect factors such as temperature mg carbonate chemistry b and salinity na the nutrient type elements ba cd and possibly zn are useful tools to reconstruct biogeochemical cycling and past ocean circulation still also nutrient type elements will be most likely influenced by factors other than their relative concentrations culturing benthic foraminifera under controlled carbonate chemistry conditions allows for disentanglement of impacts of different parameters of the carbon system on the elemental composition of foraminiferal calcite here we show that zinc incorporation in cultured specimens of the benthic foraminifer ammonia tepida is correlated to changes in carbonate ion concentration co32 by modeling activities of different chemical species of zn in seawater over a range of co32 we suggest that zn2 rather than other relatively abundant zn species e g znco30 and znhco3 is taken up during biomineralization our results suggest that foraminiferal zn ca might be especially useful when combined with other co32 proxies enabling reconstruction of past seawater element concentrations conversely when the nutrient type element concentrations are known incorporation of zn in foraminiferal shells can be used to reconstruct past sea water carbon speciation

a new boron isotope ph calibration for orbulina universa with implications for understanding and accounting for vital effects boron isotope ratios as measured in planktic foraminifera can be a useful tracer of past ocean ph and hence help to discern the concentration of co2 in the ancient atmosphere however different species of planktic foraminifera demonstrate different patterns of boron isotope variation with ambient seawater ph therefore when applying the proxy to questions in the geological past species specific calibrations are preferable beyond the evolutionary history of a calibrated species we must rely on our understanding of the causes of the observed vital effects in the modern ocean and the applicability of that understanding to extinct species here we present a new open ocean calibration of the planktic foraminifera orbulina universa measured via multi collector inductively coupled mass spectrometry mc icpms unlike other symbiont bearing foraminifera o universa record a 11b 11b and hence ph that is lower than its surrounding seawater but with a ph sensitivity roughly equal to that of aqueous borate ion we discuss the significance of this for application of the boron isotope proxy in deep time with recommendations for best practice and future research directions

millennial scale ice rafting events and hudson strait heinrich like events during the late pliocene and pleistocene a review abstract various types of abrupt millennial scale climate variability such as dansgaard oeschger and heinrich events characterized the last glacial period over the last decade a number of studies demonstrated that such millennial scale climate variability was not limited to the last glacial but inherent to quaternary climate here we review the occurrence and origin of millennial ice rafting events in the north atlantic during the late pliocene and pleistocene last 3 4 ma with a special focus on north atlantic hudson strait hs heinrich like events we show that heinrich layers 5 4 2 and 1 in marine sediment cores from across the north atlantic all bear the organic geochemical fingerprint of the hudson area using this framework and combining previously published results detailed investigations into the organic and inorganic chemistry of ice rafted debris ird found across the north atlantic demonstrate that prior to mis 16 650 ka ird in the north atlantic did not originate from the hudson area of northern canada the signature of this early ird is distinctly different compared to that of hs heinrich layers rather ice rafting events during the late pliocene and early pleistocene predominantly emanated from the calving of the greenland and fennoscandian ice sheets and possibly minor contributions from local ice streams from the north american and british ice sheets compared to north atlantic hs heinrich events these early pleistocene ird events had a limited impact on surface water characteristics in the north atlantic north atlantic hs heinrich like events first occurred during mis 16 at the same time the dominant frequency in silicate rich ird accumulation shifted from the obliquity 41 ka to a 100 ka frequency across the north atlantic iceberg survivability or a change in iceberg trajectory likely did not control this change in ird regime these results lend further support for the existing hypothesis that an increase in size thickness of the laurentide ice sheet controls the occurrence of north atlantic hs heinrich events favoring an internal dynamic mechanism for their occurrence

links between the onset of modern walker circulation and the mid pleistocene climate transition sea surface temperatures ssts reconstructed from ocean drilling program sites 806 and 849 in the western and eastern equatorial pacific provide a history of the strength of the walker circulation between 1 5 and 0 5 ma a progressive cooling in the eastern equatorial pacific is paralleled by intensification of the equatorial zonal sst gradient that began 1 17 ma prior to the expansion of global ice volume associated with the mid pleistocene climate transition the ssts in the eastern equatorial pacific and the zonal gradient reached modern values by 0 9 ma we propose that this onset and intensification of the modern walker circulation reduced heat flux but increased moisture transport to high latitudes leading to the development of more extensive ice sheets and the shift toward the 100 ka world

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

permian triassic mass extinction pulses driven by major marine carbon cycle perturbations the permian triassic boundary approximately 251 9 million years ago marked the most severe environmental crisis identified in the geological record which dictated the onwards course for the evolution of life magmatism from siberian traps is thought to have played an important role but the causational trigger and its feedbacks are yet to be fully understood here we present a new boron isotope derived seawater ph record from fossil brachiopod shells deposited on the tethys shelf that demonstrates a substantial decline in seawater ph coeval with the onset of the mass extinction in the latest permian combined with carbon isotope data our results are integrated in a geochemical model that resolves the carbon cycle dynamics as well as the ocean redox conditions and nitrogen isotope turnover we find that the initial ocean acidification was intimately linked to a large pulse of carbon degassing from the siberian sill intrusions we unravel the consequences of the greenhouse effect on the marine environment and show how elevated sea surface temperatures export production and nutrient input driven by increased rates of chemical weathering gave rise to widespread deoxygenation and sporadic sulfide poisoning of the oceans in the earliest triassic our findings enable us to assemble a consistent biogeochemical reconstruction of the mechanisms that resulted in the largest phanerozoic mass extinction the end permian mass extinction was linked with ocean acidification due to carbon degassing associated with siberian trap emplacement according to boron isotopes from fossil shells and reconstruction of the carbon cycle

a phase space model for pleistocene ice volume article i nfo we present a phase space model that simulates pleistocene ice volume changes based on earth s orbital parameters terminations in the model are triggered by a combination of ice volume and orbital forcing and agree well with age estimates for late pleistocene terminations the average phase at which model terminations begin is approximately 90 90 before the maxima in all three orbital cycles the large variability in phase is likely caused by interactions between the three cycles and ice volume unlike previous ice volume models this model produces an orbitally driven increase in 100 kyr power during the mid pleistocene transition without any change in model parameters this supports the hypothesis that pleistocene variations in the 100 kyr power of glacial cycles could be caused at least in part by changes in earth s orbital parameters such as amplitude modulation of the 100 kyr eccentricity cycle rather than changes within the climate system

influence of tectonic uplift of the qinling mountains on the paleoclimatic environment of surrounding areas insights from loess paleosol sequences weihe basin central china abstract the southern edge of the chinese loess plateau affected by the stepwise uplift of the qinling mountains is a transitional climatic area between the different climatic environments and sedimentary characteristics to the north and south sides of the qinling mountains the study of different quaternary loess deposits in this region is conducive to improving our understanding of the micro scale climatic effects of tectonic developments here we use a series of experimental methods on a well preserved loess paleosol sequence in the south jingyang plateau to obtain proxy data including grain size magnetic susceptibility loss on ignition and geochemical elemental changes in grain size magnetic susceptibility and loss on ignition indicate that the east asian monsoon has undergone significant changes due to the continued global cooling and mid pleistocene climate transition during the deposition process of xsd loess i e the intensities of the winter and summer monsoons were simultaneously enhanced elemental correlations and factor analysis indicate the sedimentary environment and provenance of the deposits while elemental enrichment and element ratios including si ti al ti rb sr and zr rb are consistent with changes in the intensity of pedogenic and of the east asian monsoon as reflected by climate proxies illustrating that xrf core scanning analysis technology has great potential in the field of quaternary environmental changes of loess furthermore the stepwise uplift of the qinling mountains which has blocked the winter and summer monsoons to a certain extent has had a significant impact on the relative degree of loess accumulation and pedogenic in the northern piedmont southern piedmont and intermontane basin of the qinling mountains and also appears to have promoted settlement by early humans hence the study of paleoclimate in areas of active tectonic movement has the potential to promote our understanding of micro scale climate change in this region in the future

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

magnetostratigraphy and authigenic 10be 9be dating of plio pleistocene abyssal surficial sediments on the southern slope of mariana trench and sedimentary processes during the mid pleistocene transition

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

atlantic overturning responses to obliquity and precession over the last 3 myr this study analyzes 39 atlantic and seven pacific benthic 13c records to characterize obliquity and precession responses in atlantic overturning since 3 ma regional benthic 13c stacks are also analyzed a major transition in orbital responses is observed at 1 5 1 6 ma coincident with the first glacial shoaling of northern component water since 1 5 ma the phases of atlantic benthic 13c records from 2300 to 4000 m depth lag maximum obliquity by 59 6 7 kyr and june perihelion precession forcing by 133 8 5 kyr comparison with north atlantic sea surface temperature suggests that these orbital responses particularly precession in middle deep atlantic 13c are associated with changes in ocean heat transport and overturning rates the mid pleistocene transition had little effect on the obliquity and precession phases of benthic 13c but did result in a 50 decrease in the obliquity power of middle deep atlantic 13c at 0 6 ma

environmental constraints on holocene cold water coral reef growth off norway insights from a multiproxy approach high latitude cold water coral cwc reefs are particularly susceptible due to enhanced co2 uptake in these regions using precisely dated u th cwcs lophelia pertusa retrieved during research cruise pos 391 lopphavet 70 6 n oslofjord 59 n we applied boron isotopes 11b ba ca li mg and u ca ratios to reconstruct the environmental boundary conditions of cwc reef growth the sedimentary record from these cwc reefs reveals a lack of corals between 6 4 and 4 8 ka the question remains if this phenomenon is related to changes in the carbonate system or other causes the initial postglacial setting had elevated ba ca ratios indicative of meltwater fluxes showing a decreasing trend towards cessation at 6 4 ka with a oscillation pattern similar to continental glacier fluctuations downcore u ca ratios reveal an increasing trend which is outside the range of modern u ca variability in l pertusa suggesting changes of seawater ph near 6 4 ka the reconstructed bwt at lopphavet reveals a striking similarity to barent sea surface and sub sea surface temperature records we infer that meltwater pulses weakened the north atlantic current system resulting in southward advances of cold and co2 rich arctic waters a corresponding shift in the 11b record from 25 0 to 27 0 probably implies enhanced ph up regulation of the cwcs due to the higher pco2 concentrations of ambient seawater which hastened mid holocene cwc reef decline on the norwegian margin

the prism pliocene palaeoclimate reconstruction time for a paradigm shift global palaeoclimate reconstructions have been invaluable to our understanding of the causes and effects of climate change but single temperature representations of the oceanic mixed layer for dat

low latitude hydro climatic changes during the plio pleistocene evidence from high resolution alkane records in the southern south china sea abstract high resolution records of long chain n alkane biomarkers from the southern south china sea reveal tightly response of n alkane distribution to hydro climate changes over the past 5 ma with increasing longer chain n c31 alkanes indicating a correlation with drier conditions and increasing shorter chain n c27 alkanes with wetter conditions the variations of the c31 c27 ratio or the alkane chain length index imply humid conditions before 2 9 ma progressively reduced moisture since then and to bigger fluctuations between wet and dry conditions since 1 2 ma this long term hydro climate trend is superimposed by glacial dry and interglacial wet patterns over the plio pleistocene glacial cycles combined with other proxy records our results indicate that precipitation over the tropical asia pacific strengthened before the onset of the northern hemisphere glaciation and the mid pleistocene climate transition at about 1 2 ma these dramatic humidity changes over major climate transitions imply a crucial role of tropical hydrology dynamics on global climate change in the late cenozoic

thermohaline circulation crisis and impacts during the mid pleistocene transition the mid pleistocene transition mpt marked a fundamental change in glacial interglacial periodicity when it increased from 41 thousand year to 100 thousand year cycles and developed higher amplitude climate variability without substantial changes in the milankovitch forcing here we document by using nd isotopes a major disruption of the ocean thermohaline circulation thc system during the mpt between marine isotope stages miss 25 and 21 at 950 to 860 thousand years ago which effectively marks the first 100 thousand year cycle including an exceptional weakening through a critical interglacial mis 23 at 900 thousand years ago its recovery into the post mpt 100 thousand year world is characterized by continued weak glacial thc the mpt ocean circulation crisis facilitated the coeval drawdown of atmospheric co2 and high latitude ice sheet growth generating the conditions that stabilized 100 thousand year cycles

controls on shell mg ca and sr ca in cultured planktonic foraminiferan globigerinoides ruber white mg ca and sr ca ratios were determined on a single species of planktonic foraminiferan globigerinoides ruber white collected from the gulf of eilat and cultured in seawater at five different salinities 32 to 44 five temperatures 18 to 30 c and four ph values 7 9 to 8 4 the mg ca temperature calibration of cultured g ruber with an exponential slope of 8 3 c agrees well with previously published calibrations from core tops and sediment traps however the dependence of mg ca on salinity with an exponential slope of 5 3 psu is also significant and should be included in the calibration equation with this purpose we calculated a calibration equation for g ruber dependent on both temperature and salinity within the 95 confidence limits mg ca mmol mol exp 0 06 0 02 s psu 0 08 0 02 t c 2 8 1 0 r2 0 95 the influence of ph on mg ca ratios is negligible at ambient seawater ph 8 1 to 8 3 however we observe a dominating ph control on shell mg ca when the ph of seawater is lower than 8 0 sr ca in g ruber shows a significant positive correlation with average growth rate presumably part of the variability in shell sr ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions

evolution of ocean temperature and ice volume through the mid pleistocene climate transition earth s climate underwent a fundamental change between 1250 and 700 thousand years ago the mid pleistocene transition mpt when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing over this time an increase occurred in the amplitude of change of deep ocean foraminiferal oxygen isotopic ratios traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep ocean temperature we have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios our results suggest that the mpt was initiated by an abrupt increase in antarctic ice volume 900 thousand years ago we see no evidence of a pattern of gradual cooling but near freezing temperatures occur at every glacial maximum

evolution of a deep water ferromanganese nodule in the south china sea in response to pacific deep water circulation and continental weathering during the plio pleistocene abstract the south china sea scs is connected to the west pacific through a deep channel in the luzon strait thus the scs deep water is sensitive to the evolution of pacific ocean circulation which significantly influences the global climate system geochemical data pb isotope and redox sensitive elements data and magnetic data were determined for a fe mn nodule obtained from jiaolong seamount in the central scs these records reflect interactions between changes in ice sheets deep pacific circulation and weathering inputs to the deep scs during the pliocene and quaternary our results show that the scs deep water environment can be divided into three major stages stages 1 3 stage 1 4 8 1 4 ma was characterized by a well oxygenated pacific deep water pdw and lower dust inputs then moderate stable deep water ventilation and greater inputs of asian dust occurred during stage 2 1 4 0 9 ma during stage 3

x ray fluorescence core scanning records of chemical weathering and monsoon evolution over the past 5 myr in the southern south china sea with benthic foraminiferal d 18 o reveal that phases of the east asian summer monsoon abruptly changed by more than 90 at 4 0 ma 2 75 ma 1 0 ma and 0 6 ma relative to global ice volume at the obliquity and the precession bands over the past 5 myr strong 400 kyr and 100 kyr cycles in the k al and ti al records consistently exist over the past 5 myr particularly these cycles are highly coherent with the long and short eccentricity cycles in the truncated insolation at 65 n indicating an eccentricity forcing of the east asian summer monsoon the chemical weathering recorded in the elemental records of odp site 1143 also shows highly coherent relationship with the ocean carbon reservoir at the eccentricity the obliquity and the precession bands over the late pliocene and pleistocene

a 20 million year record of planktic foraminiferal b ca ratios systematics and uncertainties in pco2 reconstructions we use new and published data representing a 20 million long record to discuss the systematics of interpreting planktic foraminiferal b ca ratios b ca based reconstructions of seawater carbonate chemistry and atmospheric pco 2 assume that the incorporation of boron into foraminiferal tests can be empirically described by an apparent partition coefficient k d b ca caco 3 b oh 4 hco 3 seawater hemming and hanson 1992 it has also been proposed that there is a species specific relationship between k d and temperature yu et al 2007 as we discuss although these relationships may be robust there remain significant uncertainties over the controls on boron incorporation into foraminifera it is difficult to be certain that the empirically defined correlation between temperature and k d is not simply a result of covariance of temperature and other hydrographic variables in the ocean including carbonate system parameters there is also some evidence that k d may be affected by solution hco 3 co 2 3 ratios i e ph or by co 2 3 in addition the theoretical basis for the definition of kd and for a temperature control on k d is of debate we also discuss the sensitivity of pco 2 reconstructions to different k d temperature calibrations and seawater b ca if a k d temperature calibration is estimated using ice core pco 2 values between 0 and 200 ka b ca ratios can be used to reasonably approximate atmospheric pco 2 between 200 and 800 ka however the absolute values of pco 2 calculated are sensitive to the choice of k d temperature relationship for older time periods the absolute values of pco 2 are also dependent on the evolution of seawater b concentrations however we find that over the last 20 ma reconstructed changes in declining pco 2 across the mid pleistocene transition pliocene glacial intensification and the middle miocene climate transition are supported by the b ca record even if a constant coretop k d is used or different k d temperature calibrations and models of seawater b evolution are applied to the data the inferred influence of temperature on k d from coretop data therefore cannot itself explain the structure of a published pco 2 reconstruction tripati et al 2009 we conclude the raw b ca data supports a coupling between pco 2 and climate over the past 20 ma finally we explore possible implications of b ca based pco 2 estimates for the interpretation of other marine pco 2 proxies

high resolution alkenone palaeobarometry indicates relatively stable pco2 during the pliocene 3 3 to 2 8 ma temperature reconstructions indicate that the pliocene was approximately 3 c warmer globally than today and several recent reconstructions of pliocene atmospheric co2 indicate that it was above pre industrial levels and similar to those likely to be seen this century however many of these reconstructions have been of relatively low temporal resolution meaning that these records may have failed to capture variations associated with the 41 kyr glacial interglacial cycles thought to have operated in the pliocene here we present a new high temporal resolution alkenone carbon isotope based record of pco2 spanning 3 3 2 8 ma from ocean drilling program site 999 our record is of high enough resolution approx 19 kyr to resolve glacial interglacial changes beyond the intrinsic uncertainty of the proxy method the record suggests that pliocene co2 levels were relatively stable exhibiting variation less than 55 ppm we perform sensitivity studies to investigate the possible effect of changing sea surface temperature sst which highlights the importance of accurate and precise sst reconstructions for alkenone palaeobarometry but demonstrate that these uncertainties do not affect our conclusions of relatively stable pco2 levels during this interval

evolution of antarctic intermediate water during the plio pleistocene and implications for global climate evidence from the south atlantic abstract formed in the southern ocean antarctic intermediate water aaiw plays a fundamental role in the modern climate system as an important sink for atmospheric co2 and as a mid depth conduit supplying nutrient rich waters to subtropical and tropical upwelling regions during the transition from warm pliocene greenhouse conditions to pleistocene icehouse conditions around 3 ma model simulations suggest dramatic circulation changes in the southern ocean aaiw formation region due to cooling and expanded sea ice cover around antarctica however the history and properties of aaiw over this time period are still poorly understood here we trace aaiw source water provenance temperature and salinity changes over the last 4 myr using nd isotopes of fe mn oxyhydroxide encrusted foraminifera benthic foraminiferal mg ca and stable isotopes from southwest atlantic dsdp site 516 our results show that modern aaiw properties emerged gradually over the last 3 myr as evidenced by gradual cooling 6 c and freshening of intermediate waters over this same interval end values decrease and diverge away from those of pacific sourced waters and converge on values of present day circumpolar deep water cdw these observations are in accordance with model simulations indicating increased deep vertical mixing at the polar front associated with sea ice extension these modified aaiw source waters penetrated increasingly northward into the atlantic at intermediate depths enhancing nutrient supply and contributing to surface cooling along subtropical coastal upwelling sites these circulation changes may have facilitated ocean co2 storage providing a positive feedback amplifying global cooling and intensification of northern hemisphere glaciation

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

stable carbon cycle climate relationship during the late pleistocene a record of atmospheric carbon dioxide co2 concentrations measured on the epica european project for ice coring in antarctica dome concordia ice core extends the vostok co2 record back to 650 000 years before the present yr b p before 430 000 yr b p partial pressure of atmospheric co2 lies within the range of 260 and 180 parts per million by volume this range is almost 30 smaller than that of the last four glacial cycles however the apparent sensitivity between deuterium and co2 remains stable throughout the six glacial cycles suggesting that the relationship between co2 and antarctic climate remained rather constant over this interval

the role of co2 decline for the onset of northern hemisphere glaciation the pliocene pleistocene transition ppt from around 3 2 to 2 5 million years ago ma represented a major shift in the climate system and was characterized by a gradual cooling trend and the appearance of large continental ice sheets over northern eurasia and north america paleo evidence indicates that the ppt was accompanied and possibly caused by a decrease in atmospheric co2 but the temporal resolution of co2 reconstructions is low for this period of time and uncertainties remain large therefore instead of applying existent co2 reconstructions we solved an inverse problem by finding a schematic co2 concentration scenario that allows us to simulate the temporal evolution of key climate characteristics in agreement with paleoclimate records to this end we performed an ensemble of transient simulations with an earth system model of intermediate complexity from which we derived a best guess transient co2 scenario for the interval from 3 2 to 2 4 ma that gives the best fit between the simulated and reconstructed benthic 18o and global sea surface temperature evolution our data constrained co2 scenarios are consistent with recent co2 reconstructions and suggest a gradual co2 decline from 375 425 to 275 300 ppm between 3 2 and 2 4 ma in addition to a gradual decline the best fit to paleoclimate data requires the existence of pronounced co2 variability coherent with the 41 kyr 1 kyr 1000 years obliquity cycle in our simulations the long term co2 decline is accompanied by a relatively abrupt intensification of northern hemisphere glaciation at around 2 7 ma this is the result of a threshold behaviour of the ice sheets response to gradual co2 decrease and orbital forcing the simulated northern hemisphere ice sheets during the early pleistocene glacial cycles reach a maximum volume equivalent to a sea level drop of about 40 m both ice volume and benthic 18o are dominated by 41 kyr cyclicity our simulations suggest that before 2 7 ma greenland was ice free during summer insolation maxima and only partly ice covered during periods of minimum summer insolation a fully glaciated greenland comparable to its present day ice volume is modelled only during glacial maxima after 2 7 ma and more continuously after 2 5 ma

simulating the mid pleistocene transition through regolith removal abstract quaternary 18o ice volume proxy records show a transition from high frequency small amplitude glacial cycles to low frequency large amplitude glacial cycles this reorganization of the climate system termed the mid pleistocene transition mpt is thought to reflect a change in land ice response to orbital forcing despite no significant change in orbital cycles during this period one potential explanation for the mpt proposes that gradual erosion of high latitude northern hemisphere regolith by multiple cycles of glaciation caused a transition in ice sheet response to external forcing here we explore this regolith hypothesis using a complex earth system model we show that simulating a transition from deformable sediment to crystalline bedrock produces an evolution in ice volume response similar to proxy reconstructions of the mpt the simulated change in ice volume response is due to a combination of climate and ice flow changes with crystalline bedrock producing thicker colder ice sheets that accumulate more snowfall and have a smaller ablation zone further experiments that include transient eccentricity amplifying co2 forcing show only small differences in ice response compared to those with orbital forcing only suggesting that cycles of co2 were not the primary cause of the mpt

reduced upwelling of nutrient and carbon rich water in the subarctic pacific during the mid pleistocene transition abstract reduction in atmospheric pco2 has been hypothesised as a causal mechanism for the mid pleistocene transition mpt which saw global cooling and increased duration of glacials between 0 6 and 1 2 ma sea ice modulated high latitude upwelling and ocean atmospheric co2 flux is considered a potential mechanism for pco2 decline although there are no long term nutrient upwelling records from high latitude regions to test this hypothesis using nitrogen isotopes and opal mass accumulation rates from 0 to 1 2 ma we calculate a continuous high resolution nutrient upwelling index for the bering sea and assess possible changes to regional co2 fluxes and to the relative control of sea ice sea level and glacial north pacific intermediate water gnpiw on deep mixing and nutrient upwelling in the region we find nutrient upwelling in the bering sea correlates with global ice volume and air temperature throughout the study interval from 1 ma and particularly during the 900 ka event suppressed nutrient upwelling would have lowered oceanic fluxes of co2 to the atmosphere supporting a reduction in global pco2 during the mpt this timing is consistent with a pronounced increase in sea ice during the early pleistocene and restriction of flow through the bering strait during glacials after 900 ka both of which would have acted to suppress upwelling we suggest that sea level modulated gnpiw expansion during glacials after 900 ka was the dominant control on subarctic pacific upwelling strength during the mid late pleistocene while sea ice variability played a secondary role

la mc icp ms study of boron isotopes in individual planktonic foraminifera a novel approach to obtain seasonal variability patterns abstract boron isotope 11b analysis using bulk foraminifera samples is a widely used method to reconstruct paleo sea water ph conditions although these analyses exhibit high analytical precision short term information is lost due to the pooling of tests with distinct and diverse boron isotope signatures resulting in average values for the time interval encompassed in the sample here we present and assess the analysis of 11b of individual foraminifera by means of laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms to obtain seasonal variability patterns and to test the limits of precision of la mc icp ms on the planktonic foraminifera orbulina universa the results show that relative seasonal differences of 11 can be captured from either uncleaned or cleaned individual o universa tests with an average precision of 2 9 2 se the 11b variability among foraminifera representing the same season is on average 7 4 2 sd irrespective of cleaning state with our approach analyses on oxidatively cleaned o universa do not require the use of a matrix matched standard to obtain b isotope values in the range of those expected for solution multi specimen analyses our results are useful for considering the potential spread caused by foraminifera vital effects and for obtaining information of seasonal ranges of ph and possible bias related to seasonality hidden within conventional solution based 11b analyses

the role of orbital forcing in the early middle pleistocene transition abstract the early middle pleistocene transition empt is the term used to describe the prolongation and intensification of glacial interglacial climate cycles that initiated after 900 000 years ago during the transition glacial interglacial cycles shift from lasting 41 000 years to an average of 100 000 years the structure of these glacial interglacial cycles shifts from smooth to more abrupt saw toothed like transitions despite eccentricity having by far the weakest influence on insolation received at the earth s surface of any of the orbital parameters it is often assumed to be the primary driver of the post empt 100 000 years climate cycles because of the similarity in duration the traditional solution to this is to call for a highly nonlinear response by the global climate system to eccentricity this eccentricity myth is due to an artefact of spectral analysis which means that the last 8 glacial interglacial average out at about 100 000 years in length despite ranging from 80 000 to 120 000 years with the realisation that eccentricity is not the major driving force a debate has emerged as to whether precession or obliquity controlled the timing of the most recent glacial interglacial cycles some argue that post empt deglaciations occurred every four or five precessional cycle while others argue it is every second or third obliquity cycle we review these current theories and suggest that though phase locking between orbital forcing and global ice volume may occur the chaotic nature of the climate system response means the relationship is not consistent through the last 900 000 years

the plio pleistocene development of atlantic deep water circulation and its influence on climate trends abstract using benthic stable isotope records from 10 sites in the atlantic ocean including two new records from walvis ridge in the southeast atlantic sites 1264 and 1267 we review changes in atlantic deep water circulation in the context of plio pleistocene climate overall we find non linear responses of atlantic deep water circulation to a cooling climate with differently evolving glacial and interglacial states our main conclusion is that peak north atlantic deep water nadw production was reached between 2 0 and 1 5 ma most prominently seen by a maximum in ventilated high 13 c conditions in the mid depth southeast atlantic site 1264 we infer that a major source of nadw at this time was the export of dense overflow water from the nordic seas into the abyssal east atlantic sea surface temperature records from the north and south atlantic support this notion and indicate that the peak nadw production between 2 0 and 1 5 ma was compensated by a stronger warm surface water return flow i e atlantic meridional overturning circulation amoc was enhanced causing long term 10 5 year heat piracy from the south to the north atlantic in the wider picture of plio pleistocene climate evolution we find that a long term enhancement in the average state of amoc 2 4 1 3 ma coincides with the 41 kyr world hence we speculate that the transitory negative feedback response of enhanced amoc to a cooling climate supplied heat to key areas of ice sheet growth acting to limit their size and maintain the 41 kyr world once a threshold in global cooling was reached the strength of amoc lessened providing a positive feedback for the early middle pleistocene transition and the associated build up of northern hemisphere ice sheets

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

exploring foraminiferal sr ca as a new carbonate system proxy in present day paleoclimate research one of the most pressing challenges is the reconstruction of atmospheric co2 concentrations a variety of proxies for several components of the marine inorganic carbon system have been developed in this context e g b isotopes b ca u ca to allow reconstruction of past seawater ph hco3 and co32 and thereby facilitate estimates of past atmospheric pco2 based on culture experiments using the benthic foraminifera ammonia sp we describe a positive correlation between sr ca and the carbonate system namely dic bicarbonate ion concentration foraminiferal sr ca ratios provide potentially additional constraints on the carbonate system proxy because the analysis of foraminiferal carbonate sr ca is straightforward and not easily contaminated applying our calibration to a published dataset of paleo sr ca suggests the validity of sr ca as a carbonate system proxy furthermore we explore how our data can be used to advance conceptual understanding of the foraminiferal biomineralization mechanism

the role of deep ocean circulation in setting glacial climates the glacial cycles of the pleistocene involve changes in the circulation of the deep ocean in important ways this review seeks to establish what were the robust patterns of deep sea water mass changes and how they might have influenced important parts of the last glacial cycle after a brief review of how tracers in the modern ocean can be used to understand the distribution of water masses i examine the data for biogeochemical circulation rate and conservative tracers during glacial climates some of the robust results from the literature of the last 30 years include a shoaled version of northern source deep water in the atlantic expanded southern source water in the abyss and deep ocean salt rather than heat stratification of the last glacial maximum lgm deep sea and several lines of evidence for slower overturning circulation in the southern deep cell we combine these observations into a new idea for how the ocean atmosphere system moves from interglacial to glacial periods across a single cycle by virtue of its influence on the melting of land based ice around antarctica cooling north atlantic deep water nadw leads to a cold and salty version of antarctic bottom water aabw this previously underappreciated feedback can lead to a more stratified deep ocean that operates as a more effective carbon trap than the modern helping to lower atmospheric co 2 and providing a mechanism for the deep ocean to synchronize the hemispheres in a positive feedback that drives the system to further cooling

investigation of an early pleistocene marine osmium isotope record from the eastern equatorial pacific osmium isotope composition 187os 188os and concentrations of os ir and pt are reported for an early pleistocene section from the odp site 849 in the eastern equatorial pacific using the data obtained in this study the contributions from detrital and extraterrestrial particulate matter to os concentration and 187os 188os of sediment are estimated our calculations show that detrital contributions to sedimentary os are too small 2 to significantly shift measured bulk sediment 187os 188os away from seawater values a moderate but significant negative correlation between 187os 188os and 3he 188os indicate that the average particulate extraterrestrial os flux to this site is 1 21 0 47 pg cm 2 kyr 1 which constitutes 3 of total os burial flux the estimates of detrital and extraterrestrial os are used to calculate the seawater 187os 188os in the early pleistocene the most notable features of this early pleistocene 187os 188os record are 1 glacial interglacial 187os 188os differences are insignificant within errors of estimates 2 glacial 187os 188os values are higher compared to those reported for the late pleistocene glacials comparison of 187os 188os values at site 849 to the late pleistocene records suggests that average seawater 187os 188os change has been modest 5 since the early pleistocene assuming that 187os 188os difference between the glacial periods of the late and the early pleistocene results solely from temperature dependence of weathering rates it has been calculated that average surface temperature during the late pleistocene glacials was 0 8 0 2 c lower than glacials in the early pleistocene this inference is consistent with temperature estimates based on a recent study of pco2 reconstruction in the pleistocene this observation based on limited studies of marine 187os 188os records seems to suggest that temperature played an important role in influencing chemical weathering during the pleistocene glacials however more studies are needed to confirm if this temperature weathering feedback was operational throughout the pleistocene a significant down core ir 3he co variation coupled with similar burial fluxes of ir at site 849 and at ll44 gpc 3 in the north pacific point to the utility of ir concentration as a point paleoflux tracer however a twofold difference in ir burial fluxes between the eastern and the western equatorial pacific suggests that calibration in space and time is required to use ir concentration as a robust indicator of paleoflux through time significant co variation of concentrations of os and total alkenone during the glacials coupled with lighter 13c of benthic foraminifera indicates that productivity and carbon burial played a dominant control on scavenging of os at site 849 in a broader context this data set encourages future investigation of response of pge behavior to paleoceanographic processes

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

the mid pleistocene transition in the subtropical southwest pacific 1 reconstructions of subtropical southwest pacific climate variability over the pleistocene were derived from coupled planktic foraminiferal 18o mg ca measurements taken from a southern coral sea sediment core a clear shift from 40 kyr to 100 kyr modes of reconstructed glacial interglacial sea surface temperature sst variability is seen over the mid pleistocene transition and these fluctuations are shown to have remained coherent with the orbital obliquity cycle across the transition the likely origin of this strong obliquity signal in subtropical southwest pacific sst is shown to be the southern high latitudes and comparison with existing sst reconstructions from the equatorial pacific is consistent with the communication of the signal occurring principally by greenhouse gas forcing in contrast to the sst reconstruction regional hydrological cycle variability based on the calculated local component of 18osw change does not show significant coherence with obliquity after 1000 ka the decoupling of the sst and hydrological cycle responses over the mid pleistocene transition allows constraints to be placed on the evolution and extent of orbitally paced fluctuations within the coupled low latitude ocean atmosphere system

history of seawater carbonate chemistry atmospheric co 2 and ocean acidification humans are continuing to add vast amounts of carbon dioxide co2 to the atmosphere through fossil fuel burning and other activities a large fraction of the co2 is taken up by the oceans in a process that lowers ocean ph and carbonate mineral saturation state this effect has potentially serious consequences for marine life which are however difficult to predict one approach to address the issue is to study the geologic record which may provide clues about what the future holds for ocean chemistry and marine organisms this article reviews basic controls on ocean carbonate chemistry on different timescales and examines past ocean chemistry changes and ocean acidification events during various geologic eras the results allow evaluation of the current anthropogenic perturbation in the context of earth s history it appears that the ocean acidification event that humans are expected to cause is unprecedented in the geologic past for which sufficiently well preserved records are available

upwelling intensification as part of the pliocene pleistocene climate transition a deep sea sediment core underlying the benguela upwelling system off southwest africa provides a continuous time series of sea surface temperature sst for the past 4 5 million years our results indicate that temperatures in the region have declined by about 10 c since 3 2 million years ago records of paleoproductivity suggest that this cooling was associated with an increase in wind driven upwelling tied to a shift from relatively stable global warmth during the mid pliocene to the high amplitude glacial interglacial cycles of the late quaternary these observations imply that atlantic ocean surface water circulation was radically different during the mid pliocene

the middle pleistocene transition by frequency locking and slow ramping of internal period the increase in glacial cycle length from approximately 41 to on average 100 thousand years around 1 million years ago called the middle pleistocene transition mpt lacks a conclusive explanation we describe a dynamical mechanism which we call ramping with frequency locking rfl that explains the transition by an interaction between the internal period of a self sustained oscillator and forcing that contains periodic components this mechanism naturally explains the abrupt increase in cycle length from approximately 40 to 80 thousand years observed in proxy data unlike some previously proposed mechanisms for the mpt a rapid increase in durations can be produced by a rapid change in an external parameter but this assumes rather than explains the abruptness in contrast models relying on frequency locking can produce a rapid change in durations assuming only a slow change in an external parameter we propose a scheme for detecting rfl in complex computationally expensive models and motivate the search for climate variables that can gradually increase the internal period of the glacial 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

unexpected weak seasonal climate in the western mediterranean region during mis 31 a high insolation forced interglacial marine isotope stage 31 mis 31 is an important analogue for ongoing and projected global warming yet key questions remain about the regional signature of its extreme orbital forcing and intra interglacial variability based on a new direct land sea comparison in sw iberian margin iodp site u1385 we examine the climatic variability between 1100 and 1050 ka including the super interglacial mis 31 a period dominated by the 41 ky obliquity periodicity pollen and biomarker analyses at centennial scale resolution provide new insights into the regional vegetation precipitation regime and atmospheric and oceanic temperature variability on orbital and suborbital timescales our study reveals that atmospheric and sst warmth during mis 31 was not exceptional in this region highly sensitive to precession unexpectedly this warm stage stands out as a prolonged interval of a temperate and humid climate regime with reduced seasonality despite the high insolation precession minima values forcing we find that the dominant forcing on the long term temperate forest development was obliquity which may have induced a decrease in summer dryness and associated reduction in seasonal precipitation contrast moreover this study provides the first evidence for persistent atmospheric millennial scale variability during this interval with multiple forest decline events reflecting repeated cooling and drying episodes in sw iberia our direct land sea comparison shows that the expression of the suborbital cooling events on sw iberian ecosystems is modulated by the predominance of high or low latitude forcing depending on the glacial interglacial baseline climate states severe dryness and air sea cooling is detected under the larger ice volume during glacial mis 32 and mis 30 the extreme episodes which in their climatic imprint are similar to the heinrich events are likely related to northern latitude ice sheet instability and a disruption of the atlantic meridional overturning circulation amoc in contrast forest declines during mis 31 are associated to neither sst cooling nor high latitude freshwater forcing time series analysis reveals a dominant cyclicity of about 6 ky in the temperate forest record which points to a potential link with the fourth harmonic of precession and thus low latitude insolation forcing

southern ocean temperature records and ice sheet models demonstrate rapid antarctic ice sheet retreat under low atmospheric co2 during marine isotope stage 31 abstract over the last 5 million years the earth s climate has oscillated between warm interglacial and cold glacial states some particularly warm interglacial periods i e super interglacials occurred under low atmospheric co2 and may have featured extensive antarctic ice sheet collapse here we focus on an extreme super interglacial known as marine isotope stage 31 mis31 between 1 085 and 1 055 million years ago and is the subject of intense discussion we reconstructed the first southern ocean and antarctic margin sea surface temperatures ssts from organic biomarkers and used them to constrain numerical ice sheet shelf simulations our ssts indicate that the ocean was on average 5 c 1 2 c warmer in summer than today between 50 s and the antarctic ice margin our most conservative ice sheet simulation indicates a complete collapse of the west antarctic ice sheet wais with additional deflation of the east antarctic ice sheet we suggest the wais retreated because of anomalously high southern hemisphere insolation coupled with the intrusion of circumpolar deep water onto the continental shelf under poleward intensified winds leading to a shorter sea ice season and ocean warming at the continental margin in this scenario the extreme warming we observed likely reflects the extensively modified oceanic and hydrologic system following ice sheet collapse our work highlights the sensitivity of the antarctic ice sheets to minor oceanic perturbations that could also be at play for future changes

coupling of co2 and ice sheet stability over major climate transitions of the last 20 million years the co2 content of the atmosphere has varied cyclically between 180 and 280 ppmv over the last 800 000 years closely coupled with temperature and sea level for earlier periods in earth s history pco2 is much less certain and the relationship between pco2 and climate remains poorly constrained we use boron calcium ratios in foraminifera to estimate pco2 during major climate transitions of the last 20 million years myr during the middle miocene when temperatures were 3 to 6 c

direct measurement of the boron isotope fractionation factor reducing the uncertainty in reconstructing ocean paleo ph abstract the boron isotopic composition of calcium carbonate skeletons is a promising proxy method for reconstructing paleo ocean ph and atmospheric co2 from the geological record although the boron isotope methodology has been used extensively over the past two decades to determine ancient ocean ph the actual value of the boron isotope fractionation factor e b between the two main dissolved boron species 11b oh 3 and 10b oh 4 has remained uncertain initially e b values were theoretically computed from vibrational frequencies of boron species resulting in a value of 19 later spectrophotometric ph measurements on artificial seawater suggested a higher value of 27 a few independent theoretical models also pointed to a higher e b value here we provide for the first time an independent empirical fractionation factor e b 26 0 1 0 25 c determined by direct measurements of b oh 3 in seawater and other solutions boric acid was isolated by preferential passage through a reverse osmosis membrane under controlled ph conditions we further demonstrate that applying the pitzer ion interaction approach combined with ion pairing calculations results in a more accurate determination of species distribution in aquatic solutions of different chemical composition relative to the traditional two species boron system approach we show that using the revised approach reduces both the error in simulating ancient atmospheric co2 by up to 21 and the overall uncertainty of applying boron isotopes for paleo ph reconstruction combined this revised methodology lays the foundation for a more accurate determination of ocean paleo ph through time

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

investigating controls on boron isotope ratios in shallow marine carbonates abstract the boron isotope ph proxy has been widely used to reconstruct past ocean ph values in both planktic foraminifera and corals species specific calibrations are required in order to reconstruct absolute values of ph due to the prevalence of so called vital effects physiological modification of the primary environmental signals by the calcifying organisms shallow marine abiotic carbonate e g ooids and cements could conceivably avoid any such calibration requirement and therefore provide a potentially useful archive for reconstructions in deep pre cenozoic time however shallow marine abiotic carbonates could also be affected by local shifts in ph caused by microbial photosynthesis and respiration something that has up to now not been fully tested in this study we present boron isotope measurements from shallow modern marine carbonates from the bahama bank and belize to investigate the potential of using shallow water carbonates as ph archives and to explore the role of microbial processes in driving nominally abiogenic carbonate deposition for bahama bank samples our boron based ph estimates derived from a range of carbonate types i e ooids peloids hardground cements carbonate mud stromatolitic micrite and calcified filament micrite are higher than the estimated modern mean annual seawater ph values for this region furthermore the majority 73 of our marine carbonate based ph estimates fall out of the range of the estimated pre industrial seawater ph values for this region in shallow sediment cores we did not observe a correlation between measured pore water ph and boron derived ph estimates suggesting boron isotope variability is a depositional rather than early diagenetic signal for belize reef cements conversely the ph estimates are lower than likely in situ seawater ph at the time of cement formation this study indicates the potential for complications when using shallow marine non skeletal carbonates as marine ph archives in addition variability in 11b based ph estimates provides additional support for the idea that photosynthetic co2 uptake plays a significant role in driving carbonate precipitation in a wide range of shallow water carbonates

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