a chronology of landslide activity in the valley of riviere du gouffre charlevoix quebec data on earthquake induced landslides in the valley of riviere du gouffre in the charlevoix region of quebec are presented a set of 37 radiocarbon dates obtained from tree trunks buried in flow material and found at the bottom of a small lake was used to reconstruct landslide activity in addition large subfossil tree trunks were sampled for tree ring analysis the radiocarbon dates indicate that most landslide activity in the area is recent 600 bp two tree ring dated landslides were triggered by a large earthquake in ad 1663

a modeling assessment of the interplay between aeolian iron fluxes and iron binding ligands in controlling carbon dioxide fluctuations during antarctic warm events 1 we add a prognostic biogeochemical model to the bern3d ocean circulation model to test the impact of increased aeolian iron fluxes in various regions of the ocean on long time scales atmospheric co2 is most sensitive when modern dust flux is increased 100 fold in the southern ocean for 1000 years resulting in a reduction of 10 ppmv seeding the indian ocean and south pacific results in increased export production and co2 drawdown in the southern ocean due to interbasinal transport of iron the non sea salt calcium record from dome c antarctica is used to scale aeolian iron deposition in the southern ocean in transient simulations over four antarctic warm events of the last glacial period our results suggest changes in dust flux to the southern ocean played a limited role in modulating co2 variations the impact of iron fluxes on co2 is dependent on parameter values chosen for the iron binding ligand

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

deep water formation in the north pacific and deglacial co2 rise deep water formation in the north atlantic and southern ocean is widely thought to influence deglacial co 2 rise and climate change here we suggest that deep water formation in the north pacific may also play an important role we present paired radiocarbon and boron isotope data from foraminifera from sediment core md02 2489 at 3640 m in the north east pacific these show a pronounced excursion during heinrich stadial 1 with benthic planktic radiocarbon offsets dropping to 350 years accompanied by a decrease in benthic 11 b we suggest that this is driven by the onset of deep convection in the north pacific which mixes young shallow waters to depth old deep waters to the surface and low ph water from intermediate depths into the deep ocean this deep water formation event was likely driven by an increase in surface salinity due to subdued atmospheric monsoonal freshwater flux during heinrich stadial 1 the ability of north pacific deep water npdw formation to explain the excursions seen in our data is demonstrated in a series of experiments with an intermediate complexity earth system model these experiments also show that breakdown of stratification in the north pacific leads to a rapid 30 ppm increase in atmospheric co 2 along with decreases in atmospheric 13 c and 14 c consistent with observations of the early deglaciation our inference of deep water formation is based mainly on results from a single sediment core and our boron isotope data are unavoidably sparse in the key hs1 interval so this hypothesis merits further testing however we note that there is independent support for breakdown of stratification in shallower waters during this period including a minimum in 15 n younging in intermediate water 14 c and regional warming we also re evaluate deglacial changes in north pacific productivity and carbonate preservation in light of our new data and suggest that the regional pulse of export production observed during the bolling allerod is promoted by relatively stratified conditions with increased light availability and a shallow potent nutricline overall our work highlights the potential of npdw formation to play a significant and hitherto unrealized role in deglacial climate change and co 2 rise

constraint of the co2 rise by new atmospheric carbon isotopic measurements during the last deglaciation 1 the causes of the 80 ppmv increase of atmospheric carbon dioxide co2 during the last glacial interglacial climatic transition remain debated we analyzed the parallel evolution of co2 and its stable carbon isotopic ratio 13co2 in the european project for ice coring in antarctica epica dome c ice core to bring additional constraints agreeing well but largely improving the taylor dome ice core record of lower resolution our 13co2 record is characterized by a w shape with two negative 13co2 excursions of 0 5 during heinrich 1 and younger dryas events bracketing a positive 13co2 peak during the bolling allerod warm period the comparison with marine records and the outputs of two c cycle box models suggest that changes in southern ocean ventilation drove most of the co2 increase with additional contributions from marine productivity changes on the initial co2 rise and 13co2 decline and from rapid vegetation buildup during the co2 plateau of the bolling allerod

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

thermodynamic influences on the marine carbon isotope record air sea exchange represents an important controlling factor for the distribution of carbon isotopes in the modern ocean even below the surface mixed layer here we show that this thermodynamic influence varies between water masses with a magnitude which is large relative to the amplitude of typical deep sea sediment 13c records thus changes in air sea exchange processes must be regarded as a significant source of variability for any marine 13c signal

impact of oceanic reorganizations on the ocean carbon cycle and atmospheric carbon dioxide content a zonally averaged circulation biogeochemical ocean model is used to explore how the distribution of po4 and 13c in the major basins and the atmospheric pco2 respond to rapid changes in the thermohaline circulation thc different evolutions of the atlantic thc are simulated by applying surface freshwater pulses typical for example of heinrich events and the last deglaciation in the model when the thc completely collapses po4 increases 0 5 mmol m 3 and 13c decreases 1 because of a longer residence time of waters at the surface these surface anomalies are propagated to the bottom north atlantic when the thc resumes when the thermohaline overturning is only partly reduced and at shallower depths changes in bottom waters are accompanied by a po4 decrease and 13c increase at intermediate levels in the mid latitude atlantic this results in enhanced vertical gradients of these properties consistent with chemical and isotopic reconstructions for the last glacial maximum finally the atmospheric pco2 increases during the cold period in the north atlantic when the thc is reduced with an amplitude 7 30 atm and timescale 10 to 1 2 10 yr depending on the intensity of the thc change this is qualitatively consistent with recent data from an antarctic ice core documenting a pco2 increase during the younger dryas and after heinrich events 4 and 5

atlantic pacific seesaw and its role in outgassing co2 during heinrich events 1 paleoproxy records indicate that a marked weakening of the atlantic meridional overturning circulation amoc during heinrich events was often accompanied by a notable atmospheric co2 increase however previous modeling studies display conflicting atmospheric co2 responses to an amoc shutdown here we use model simulations combined with paleoproxy records to show that depending on the deep and bottom water transport in the northern and southern pacific ocean during an amoc weakening the ocean can act either as a sink or a source of carbon results from idealized meltwater experiments as well as from a transient experiment covering heinrich stadial 4 suggest that a shutdown of the amoc during heinrich stadials 4 hs4 and 1 hs1 led to an enhancement of antarctic bottom water aabw and north pacific deep water npdw transport we show that enhanced deep and bottom water transport in the pacific ocean ventilates deep pacific carbon through the southern ocean thus contributing to a rise in atmospheric co2 this mechanism yields a good agreement between paleoproxy records and modeling results thus highlighting the possible establishment of an atlantic pacific seesaw during heinrich stadials enhanced aabw and npdw transport could account for most of the observed atmospheric co2 increase during hs4 and for about 30 of the atmospheric co2 increase during hs1

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

deepwater formation in the north pacific during the last glacial termination between approximately 17 500 and 15 000 years ago the atlantic meridional overturning circulation weakened substantially in response to meltwater discharges from disintegrating northern hemispheric glacial ice sheets the global effects of this reorganization of poleward heat flow in the north atlantic extended to antarctica and the north pacific here we present evidence from north pacific paleo surface proxy data a compilation of marine radiocarbon age ventilation records and global climate model simulations to suggest that during the early stages of the last glacial termination deep water extending to a depth of approximately 2500 to 3000 meters was formed in the north pacific a switch of deepwater formation between the north atlantic and the north pacific played a key role in regulating poleward oceanic heat transport during the last glacial termination

the impact of atmospheric pco2 on carbon isotope ratios of the atmosphere and ocean it is well known that the equilibration timescale for the isotopic ratios 13c 12c and 14c 12c in the ocean mixed layer is on the order of a decade 2 orders of magnitude slower than for oxygen less widely appreciated is the fact that the equilibration timescale is quite sensitive to the speciation of dissolved inorganic carbon dic in the mixed layer scaling linearly with the ratio dic co2 which varies inversely with atmospheric pco2 although this effect is included in models that resolve the role of carbon speciation in air sea exchange its role is often unrecognized and it is not commonly considered in the interpretation of carbon isotope observations here we use a global three dimensional ocean model to estimate the redistribution of the carbon isotopic ratios between the atmosphere and ocean due solely to variations in atmospheric pco2 under last glacial maximum lgm pco2 atmospheric 14c is increased by 30 due to the speciation change all else being equal raising the surface reservoir age by about 250 years throughout most of the ocean for 13c enhanced surface disequilibrium under lgm pco2 causes the upper ocean atmosphere and north atlantic deep water 13c to become at least 0 2 higher relative to deep waters ventilated by the southern ocean conversely under high pco2 rapid equilibration greatly decreases isotopic disequilibrium as a result during geological periods of high pco2 vertical 13c gradients may have been greatly weakened as a direct chemical consequence of the high pco2 masquerading as very well ventilated or biologically dead strangelove oceans the ongoing anthropogenic rise of pco2 is accelerating the equilibration of the carbon isotopes in the ocean lowering atmospheric 14c and weakening 13c gradients within the ocean to a degree that is similar to the traditional fossil fuel suess effect

the influence of air sea exchange on the isotopic composition of oceanic carbon observations and modeling although the carbon isotropic composition of ocean waters after they leave the surface ocean is determined by biological cycling air sea exchange affects the carbon isotopic composition of surface waters in two ways the equilibrium fractionation between oceanic and atmospheric carbon increases with decreasing temperature in southern ocean surface waters this isotopic equilibrium enriches delta sup 13 c relative to the delta sup 13 c expected from uptake and release of carbon by biological processes alone similarly surface waters in the subtropical gyres are depleted in delta sup 13 c due to extensive air sea exchange at warm temperatures countering the tendency toward isotopic equilibration with the atmosphere a relatively slow process are the effects of the equilibration of co sub 2 itself a much faster process in regions where there is a net transfer of isotopically light co sub 2 from the ocean to the atmosphere e g the equator surface waters become enriched in sup 13 c whereas in regions where isotopically light co sub 2 is entering the ocean e g the north atlantic surface waters become depleted in sup 13 c a compilation of high quality oceanic delta sup 13 c measurements along with experiments performed using a zonally averaged three basin dynamic ocean model are used to explore these processes 40 refs 14more figs 1 tab less

atmospheric δ13co2 and its relation to pco2 and deep ocean δ13c during the late pleistocene the ratio of the stable carbon isotopes of atmospheric co2 13co2 contains valuable information on the processes which are operating on the global carbon cycle however current 13co2 ice core records are still limited in both resolution and temporal coverage as well as precision in this study we performed simulations with the carbon cycle box model bicycle with special emphasis on atmospheric 13co2 proposing how changes in 13co2 might have evolved over the last 740 000 years we furthermore analyze the relationship between atmospheric 13co2 pco2 and deep ocean 13c of dissolved inorganic carbon dic 13cdic in both our modeling framework and proxy records when available our analyses show that mean ocean and deep pacific 13cdic are mainly controlled by the glacial interglacial uptake and release of carbon temporarily stored in the terrestrial biosphere during warmer climate periods in contrast glacial interglacial changes in pco2 and 13co2 represent mainly a mixture of ocean related processes superimposed on the slow glacial interglacial change in terrestrial carbon storage the different processes influencing atmospheric 13co2 largely compensate each other and cancel all variability with frequencies of 1 100 kyr 1 large excursions in 13co2 can a priori be expected as any small phase difference between the relative timing of the dominant and opposite sign processes might create large changes in 13co2 amplitudes in 13co2 caused by fast terrestrial uptake or release during millennial scale climate variability depend not only on the amount of transferred carbon but also on the speed of these changes those which occur on timescales shorter than a millennium are not detectable in 13co2 because of gas exchange equilibration with the surface ocean the 13co2 signal of fast processes on the other hand is largely attenuated in ice core records during the firnification and gas enclosure we therefore suggest to measure 13co2 with priority on ice cores with high temporal resolution and select times with rather fast climatic changes

temperature differences between the hemispheres and ice age climate variability 1 the earth became warmer and cooler during the ice ages along with changes in the earth s orbit but the orbital changes themselves are not nearly large enough to explain the magnitude of the warming and cooling atmospheric co2 also rose and fell but again the co2 changes are rather small in relation to the warming and cooling so how did the earth manage to warm and cool by so much here we argue that for the big transitions at least the earth did not warm and cool as a single entity rather the south warmed instead at the expense of a cooler north through massive redistributions of heat that were set off by the orbital forcing oceanic co2 was vented up to the atmosphere by the same redistributions the north then warmed later in response to higher co2 and a reduced albedo from smaller ice sheets this form of north south displacement is actually very familiar as it is readily observed during the younger dryas interval 13 000 years ago and in the various millennial scale events over the last 90 000 years

north pacific climate response to freshwater forcing in the subarctic north atlantic oceanic and atmospheric pathways abstract sudden changes of the atlantic meridional overturning circulation amoc are believed to have caused large abrupt climate changes over many parts of the globe during the last glacial and deglacial period this study investigates the mechanisms by which a large freshwater input to the subarctic north atlantic and an attendant rapid weakening of the amoc influence north pacific climate by analyzing four different ocean atmosphere coupled general circulation models gcms under present day or preindustrial boundary conditions when the coupled gcms are forced with a 1 sv sv 106 m3 s 1 freshwater flux anomaly in the subarctic north atlantic the amoc nearly shuts down and the north atlantic cools significantly the south atlantic warms slightly shifting the atlantic intertropical convergence zone southward in addition to this atlantic ocean atmosphere response all of the models exhibit cooling of the north pacific especially along the oceanic frontal zone consistent with paleoclimate recons

deconstructing the last glacial termination the role of millennial and orbital scale forcings using an earth system model of intermediate complexity forced by continuously varying boundary conditions and a hypothetical profile of freshwater forcing the model simulates heinrich event 1 h1 the bolling warm period the older dryas the antarctic cold reversal acr and the younger dryas in close agreement with paleo proxy data from different regions worldwide the acr can be simulated as the bipolar seesaw response to the amoc recovery during the termination of h1 however this study also demonstrates that the amplitude of the acr can be further amplified by a rapid deglacial retreat of the antarctic ice sheets we suggest that melting from both the laurentide and the antarctic ice sheets contributed to the sea level rise associated with meltwater pulse 1 a mwp 1a it is hypothesized that the northern hemispheric source of mwp 1a caused the older dryas cooling in the northern hemisphere whereas the southern hemispheric source contributed to the acr the study also documents that for the majority of paleo climate proxies considered here the relative timing can be qualitatively reproduced by the transient modeling experiments the climate model solution presented here may provide a means to further constrain dating uncertainties of some of paleo climate proxies during the last glacial termination

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

the 13c record for atmospheric co2 what is it trying to tell us abstract records of the 13c to 12c ratio of atmospheric co2 13catm trapped in antarctic ice may offer important insights into past changes in the carbon cycle and drivers of past fluctuations in atmospheric pco2 a recently published record offers the highest resolution 13catm record to date covering the last deglaciation schmitt et al 2012 two features are of particular interest one is the small magnitude 0 15 0 05 of the 13catm difference between the last glacial maximum lgm and the holocene the other is the abrupt drop 0 30 0 05 in 13catm between 17 5 and 16 0 ka this drop is coincident with that of dust deposition on the antarctic ice cap and into the ocean off south australia consistent with the hypothesis that increased efficiency of southern ocean nutrient utilization during the last glacial period and the consequent reduction in atmospheric pco2 was driven in part by dust related iron fertilization however in order to further explore either the small lgm holocene difference or the rapid drop during the early deglaciation 13catm changes related to the lgm cooling the lgm upper ocean 13c change ocean circulation changes and the lgm change in the photosynthetic fractionation factor must be known as each is currently the subject of a sizable uncertainty we present only a roadmap regarding what must be done in order to interpret the schmitt et al 2012 record

how important are southern hemisphere wind changes for low glacial carbon dioxide a model study 1 the response of atmospheric co2 to modifications in the strength and position of southern hemisphere westerlies is examined with the bern3d ocean model the model responds more sensitively to changes in the wind amplitude than to variations in latitudinal position depending on the model setup a 50 reduction in wind strength leads to a co2 drawdown of 3 34 ppm while a 50 increase results in a rise of 10 24 ppm a poleward shift of 5 lowers co2 by 2 16 ppm whereas an equatorward shift of 5 induces a co2 increase of 2 14 ppm physical and biological mechanisms equally contribute to the modeled changes in atmospheric co2 our results are in conflict with the hypothesis that southern hemisphere wind changes are responsible for the low atmospheric co2 concentrations during glacial periods

impact of oceanic circulation changes on atmospheric δ13co2 co measured in antarctic ice cores provides constraints on oceanic and terrestrial carbon cycle processes linked with millennial scale changes in atmospheric co however the interpretation of co is not straight forward using carbon isotope enabled versions of the loveclim and bern3d models we perform a set of sensitivity experiments in which the formation rates of north atlantic deep water nadw north pacific deep water npdw antarctic bottom water aabw and antarctic intermediate water aaiw are varied we study the impact of these circulation changes on atmospheric co as well as on the oceanic co distribution in general we find that the formation rates of aabw nadw npdw and aaiw are negatively correlated with changes in co namely strong oceanic ventilation decreases atmospheric co however since large scale oceanic circulation reorganizations also impact nutrient utilization and the earth s climate the relationship between atmospheric co levels and ocean ventilation rate is not unequivocal in both models atmospheric co is very sensitive to changes in aabw formation rates increased aabw formation enhances the transport of low co waters to the surface and decreases atmospheric co by contrast the impact of nadw changes on atmospheric co is less robust and might be model dependent this results from complex interplay between global climate carbon cycle and the formation rate of nadw a water body characterized by relatively high co

controls on c s ratios in hemipelagic upwelling sediments the relationship between organic carbon and reduced sulfur concentrations was investigated in hemipelagic sediments underlying highly productive regions of the ocean and oxic to suboxic waters the benguela upwelling area peru and oman margins at all three sites the degree of pyritization averaged close to 0 4 indicating that reactive iron was probably not limiting for pyrite formation complete sulfate reduction occurred in the upper sections of the sediments from the oman and peru margins however dissolved sulfate never decreased below 5 mm in the benguela upwelling sediments the authors attribute this to more advanced organic matter degradation at the benguela upwelling site c s ratios increased with increasing organic carbon concentrations at all sites for sediments with greater than 3 wt toc the c s ratio averaged about 1 3 and 1 8 times the normal marine ratio of 2 8 at the benguela upwelling and peru margin sites respectively but 2 9 times this value in the oman margin sediments they hypothesize that the quality of the organic matter undergoing burial and rates of near interfacial transport processes are the dominant controls on sulfur burial in these sediments

a coupled dynamical ocean energy balance atmosphere model for paleoclimate studies abstract the bern3d coupled three dimensional dynamical ocean energy balance atmosphere model is introduced and the atmospheric component is discussed in detail the model is of reduced complexity developed to perform extensive sensitivity studies and ensemble simulations extending over several glacial interglacial cycles on large space scales the modern steady state of the model compares well with observations in a first application several 800 000 yr simulations with prescribed orbital greenhouse gas and ice sheet forcings are performed the model shows an increase of atlantic meridional overturning circulation strength at glacial inceptions followed by a decrease throughout the glaciation and ending in a circulation at glacial maxima that is weaker than at present the sensitivity of ocean temperature to atmospheric temperature atlantic meridional overturning circulation amoc and antarctic bottom water aabw strength is analyzed at 23 locations in a second application the climate sensitivi

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

contribution of enhanced antarctic bottom water formation to antarctic warm events and millennial scale atmospheric co2 increase abstract during marine isotope stage 3 the atlantic meridional overturning circulation amoc weakened significantly on a millennial time scale leading to greenland stadials ice core records reveal that each greenland stadial is associated with a warming over antarctica so called antarctic isotope maximum aim and that atmospheric co 2 increases with antarctic temperature during the long greenland stadials here we perform transient simulations spanning the period 50 34 ka b p with two earth system models loveclim and the uvic escm to understand the possible link between changes in the amoc changes in high latitude southern hemispheric climate and evolution of atmospheric co 2 we find that oceanic carbon releases due to the amoc resumption during stadial interstadial transitions lead to an atmospheric co 2 increase however the atmospheric co 2 increases observed during the first parts of aim12 47 6 ka b p and aim8 39 8 ka b p occur during periods of weak amoc hs5 and hs4 respectively and could instead be explained by enhanced antarctic bottom water transport enhanced antarctic bottom water formation is shown to effectively ventilate the deep pacific carbon and lead to co 2 outgassing into the atmosphere in addition changes in the amoc alone are not sufficient to explain the largest antarctic isotope maxima namely aim12 and aim8 stronger formation of antarctic bottom water during aim12 and aim8 would enhance the southern high latitude warming and lead to a better agreement with high southern latitude paleoproxy records the robustness of this southern warming response is tested using an eddy permitting coupled ocean sea ice model we show that stronger antarctic bottom water formation contributes to southern ocean surface warming by increasing the southern ocean meridional heat transport

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation

a revised 1000 year atmospheric δ13c co2 record from law dome and south pole antarctica 1 we present new measurements of 13c of co2 extracted from a high resolution ice core from law dome east antarctica together with firn measurements performed at law dome and south pole covering the last 150 years our analysis is motivated by the need to better understand the role and feedback of the carbon c cycle in climate change by advances in measurement methods and by apparent anomalies when comparing ice core and firn air 13c records from law dome and south pole we demonstrate improved consistency between law dome ice south pole firn and the cape grim tasmania atmospheric 13c data providing evidence that our new record reliably extends direct atmospheric measurements back in time we also show a revised version of early 13c measurements covering the last 1000 years with a mean preindustrial level of 6 50 finally we use a kalman filter double deconvolution to infer net natural co2 fluxes between atmosphere ocean and land which cause small 13c deviations from the predominant anthropogenically induced 13c decrease the main features found from the previous 13c record are confirmed including the ocean as the dominant cause for the 1940 a d co2 leveling our new record provides a solid basis for future investigation of the causes of decadal to centennial variations of the preindustrial atmospheric co2 concentration those causes are of potential significance for predicting future co2 levels and when attempting atmospheric verification of recent and future global carbon emission mitigation measures through coupled climate carbon cycle models