isotopically depleted carbon in the mid depth south atlantic during the last deglaciation 1 the initial rise in atmospheric co2 during the last deglaciation was likely driven by input of carbon from a 13c depleted reservoir here we show that high resolution benthic foraminiferal records from the mid depth brazil margin display an abrupt drop in 13c during heinrich stadial 1 hs1 that is similar to but larger than in the atmosphere comparing the brazil margin results to published records from the north atlantic we are unable to account for the south atlantic 13c data with conservative mixing between northern and southern component water masses rapid input of abyssal water from the southeast atlantic could account for deglacial 13c anomalies at the brazil margin but it would require a reversal in deep water flow direction compared to today a new mid depth water mass may explain similar hs1 13c values in both the north and south atlantic but contrasting oxygen isotopic values between the two basins do not support such a scenario instead it appears that 13c behaved non conservatively during the deglaciation possibly reflecting the input of carbon from an isotopically depleted source

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

deglacial radiocarbon history of tropical atlantic thermocline waters absence of co2 reservoir purging signal abstract a current scenario to explain much of the atmospheric co 2 increase during the glacial to holocene climate transition requires the outgassing of a deep old oceanic co 2 reservoir thought to be located in the southern ocean in this scenario co 2 rich and 14 c depleted subsurface antarctic sourced water ventilates the thermocline where it is purged to the atmosphere in the equatorial regions a view that has been met with conflicting results using a novel approach paired surface and deep dwelling planktonic foraminifer radiocarbon analyses we document that the equatorial atlantic thermocline did not see old 14 c depleted water which would be characteristic of the proposed isolated deep ocean co 2 reservoir data from several studies concur that during the deglaciation antarctic intermediate waters were contributing to atlantic thermocline waters even more than today therefore our observations challenge the current purging hypothesis together with other studies these results suggest that the mechanism responsible for the deglacial co 2 rise cannot invoke contemporary circulation modes and or thermocline ventilation pathways

episodic reductions in bottom water currents since the last ice age although north atlantic deep water formation was greatly reduced during the last glacial maximum bottom water currents were as vigorous as at present however they were weakened during periods of north atlantic surface freshening a strong correlation can be seen between bottom water current strength and greenland air temperature records thus confirming a close connection between ocean circulation and abrupt climate change past changes in the freshwater balance of the surface north atlantic ocean are thought to have influenced the rate of deep water formation and consequently climate1 2 although water mass proxies are generally consistent with an impact of freshwater input on meridional overturning circulation3 there has been little dynamic evidence to support this linkage here we present a 25 000 year record of variations in sediment grain size from south of iceland which indicates vigorous bottom water currents during both the last glacial maximum and the holocene period together with reconstructions of north atlantic water mass distribution vigorous bottom currents suggest a shorter residence time of northern source waters during the last glacial maximum relative to the holocene period the most significant reductions in flow strength occur during periods that have been associated with freshening of the surface north atlantic the short term deglacial oscillations in bottom current strength are closely coupled to changes in greenland air temperature with a minimum during the younger dryas cold reversal and a maximum at the time of rapid warming at the onset of the holocene our results support a strong connection between ocean circulation and rapid climate change

the deglacial evolution of north atlantic deep convection deepwater formation in the north atlantic by open ocean convection is an essential component of the overturning circulation of the atlantic ocean which helps regulate global climate we use water column radiocarbon reconstructions to examine changes in northeast atlantic convection since the last glacial maximum during cold intervals we infer a reduction in open ocean convection and an associated incursion of an extremely radiocarbon 14c depleted water mass interpreted to be antarctic intermediate water comparing the timing of deep convection changes in the northeast and northwest atlantic we suggest that despite a strong control on greenland temperature by northeast atlantic convection reduced open ocean convection in both the northwest and northeast atlantic is necessary to account for contemporaneous perturbations in atmospheric circulation

the cause of carbon isotope minimum events on glacial terminations the occurrence of carbon isotope minima at the beginning of glacial terminations is a common feature of planktic foraminifera carbon isotopic records from the indo pacific sub antarctic and south atlantic we use the 13 c record of a thermocline dwelling foraminifera neogloboquadrina dutertrei and surface temperature estimates from the eastern equatorial pacific to demonstrate that the onset of 13 c minimum events and the initiation of southern ocean warming occurred simultaneously timing agreement between the marine record and the 13 c minimum in an antarctic atmospheric record suggests that the deglacial events were a response to the breakdown of surface water stratification renewed circumpolar deep water upwelling and advection of low 13 c waters to the convergence zone at the sub antarctic front on the basis of age agreement between the absolute 13 c minimum in surface records and the shift from low to high 13 c in the deep south atlantic we suggest that the 13 c rise that marks the end of the carbon isotope minima was due to the resumption of north atlantic deep water influence in the southern ocean

southwest atlantic water mass evolution during the last deglaciation the rise in atmospheric co2 during heinrich stadial 1 hs1 14 5 17 5 kyr b p may have been driven by the release of carbon from the abyssal ocean model simulations suggest that wind driven upwelling in the southern ocean can liberate 13c depleted carbon from the abyss causing atmospheric co2 to increase and the 13c of co2 to decrease one prediction of the southern ocean hypothesis is that water mass tracers in the deep south atlantic should register a circulation response early in the deglaciation here we test this idea using a depth transect of 12 cores from the brazil margin we show that records below 2300 m remained 13c depleted until 15 kyr b p or later indicating that the abyssal south atlantic was an unlikely source of light carbon to the atmosphere during hs1 benthic 18o results are consistent with abyssal south atlantic isolation until 15 kyr b p in contrast to shallower sites the depth dependent timing of the 18o signal suggests that correcting 18o for ice volume is problematic on glacial terminations new data from 2700 to 3000 m show that the deep sw atlantic was isotopically distinct from the abyss during hs1 as a result we find that mid depth 13c minima were most likely driven by an abrupt drop in 13c of northern component water low 13c at the brazil margin also coincided with an 80 decrease in 14c our results are consistent with a weakening of the atlantic meridional overturning circulation and point toward a northern hemisphere trigger for the initial rise in atmospheric co2 during hs1

the timing of deglacial circulation changes in the atlantic 1 well dated benthic foraminifer oxygen isotopic records 18o from different water depths and locations within the atlantic ocean exhibit distinct patterns and significant differences in timing over the last deglaciation this has two implications on the one hand it confirms that benthic 18o cannot be used as a global correlation tool with millennial scale precision but on the other hand the combination of benthic isotopic records with independent dating provides a wealth of information on past circulation changes comparing new south atlantic benthic isotopic data with published benthic isotopic records we show that 1 circulation changes first affected benthic 18o in the 1000 2200 m range with marked decreases in benthic 18o taking place at 17 5 cal kyr b p ka due to the southward propagation of brine waters generated in the nordic seas during heinrich stadial 1 hs1 cold period 2 the arrival of 18o depleted deglacial meltwater took place later at deeper north atlantic sites 3 hydrographic changes recorded in north atlantic cores below 3000 m during hs1 do not correspond to simple alternations between northern and southern sourced water but likely reflect instead the incursion of brine generated deep water of northern as well as southern origin and 4 south atlantic waters at 44 s and 3800 m depth remained isolated from better ventilated northern sourced water masses until after the resumption of north atlantic deep water nadw formation at the onset of the bolling allerod which led to the propagation of nadw into the south atlantic

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

a review of earthquake statistics fault and seismicity based models etas and bass there are two fundamentally different approaches to assessing the probabilistic risk of earthquake occurrence the first is fault based the statistical occurrence of earthquakes is determined for mapped faults the applicable models are renewal models in that a tectonic loading of faults is included the second approach is seismicity based the risk of future earthquakes is based on the past seismicity in the region these are also known as cluster models an example of a cluster model is the epidemic type aftershock sequence etas model in this paper we discuss an alternative branching aftershock sequence bass model in the bass model an initial or seed earthquake is specified the subsequent earthquakes are obtained from statistical distributions of magnitude time and location the magnitude scaling is based on a combination of the gutenberg richter scaling relation and the modified bath s law for the scaling relation of aftershock magnitudes relative to the magnitude of the main earthquake omori s law specifies the distribution of earthquake times and a modified form of omori s law specifies the distribution of earthquake locations unlike the etas model the bass model is fully self similar and is not sensitive to the low magnitude cutoff

ice shelf collapse from subsurface warming as a trigger for heinrich events episodic iceberg discharge events from the hudson strait ice stream hsis of the laurentide ice sheet referred to as heinrich events are commonly attributed to internal ice sheet instabilities but their systematic occurrence at the culmination of a large reduction in the atlantic meridional overturning circulation amoc indicates a climate control we report mg ca data on benthic foraminifera from an intermediate depth site in the northwest atlantic and results from a climate model simulation that reveal basin wide subsurface warming at the same time as large reductions in the amoc with temperature increasing by approximately 2 c over a 1 2 kyr interval prior to a heinrich event in simulations with an ocean model coupled to a thermodynamically active ice shelf the increase in subsurface temperature increases basal melt rate under an ice shelf fronting the hsis by a factor of approximately 6 by analogy with recent observations in antarctica the resulting ice shelf loss and attendant hsis acceleration would produce a heinrich event

glacial interglacial differences in circulation and carbon cycling within the upper western north atlantic we investigated glacial interglacial changes in the circulation and carbon cycling in the western north atlantic subtropical gyre using hydrographic data and downcore records of the stable isotopic compositions of individual shells of bahamian benthic foraminifera potential temperature salinity depth relations show that modern thermocline 200 1000 m and deep 1000 2000 m waters in the providence channels bahamas originate in the sargasso sea and are typical of the subtropical gyre gradients in the stable isotopic compositions of late holocene planulina and cibicidoides species from the bank margins 400 to 1500 m depth reflect temperature nutrient and isotopic gradients of modern subtropical gyre waters the difference between the 18o of glacial maximum and late holocene foraminifera is 2 1 for the upper 900 m of the water column and 1 6 for deeper waters indicating that these waters were 4 c and 2 c cooler respectively during glacial time the glacial temperature gradient dt dz was similar to today while the base of the thermocline was 100 m shallower these results differ significantly from our earlier results from multiple shell 18o analyses which implied upper thermocline waters were only 1 c cooler and dt dz was greater during the glacial maximum the difference occurs because bioturbation adversely affects multiple shell analyses of glacial aged samples from shallow water depths at all depths above 1500 m foraminiferal 13c are greater during the glacial maximum than the late holocene by at least 0 1 to 0 2 as much as 0 6 in the lower thermocline indicating that nutrient concentrations throughout the thermocline were reduced and there was no oxygen minimum zone during the glacial maximum this suggests greater more uniform ventilation of the thermocline results of single and multiple shell 13c analyses of glacial age foraminifera compare favorably because samples most affected by mixing correspond to water depths where the glacial interglacial change of 13c was small cooler upper ocean waters during the glacial maximum reflect cooler temperatures at the ocean surface where isopycnal surfaces outcrop including large areas of the subtropical ocean a shallower thermocline base is consistent with southward migration of the northern edge of the subtropical gyre or increased mode water production enhanced thermocline ventilation is consistent with more vigorous winds and all isopycnal surfaces outcropping in the area of ekman downwelling

carbon isotope composition of tropical surface water during the past 22 000 years carbon isotope values of many species of planktonic foraminifera are size dependant values of 13c of individual size fractions are therefore an integration of low 13c values of calcite precipitated in the juvenile growth stage and high values precipitated in later stages in general the selection of a particular size fraction for downcore studies has been subjective analysis of different size fractions of planktonic foraminifera however yields different time series in downcore studies by measuring the 13c of many size fractions the 13c precipitated throughout the growth of the foraminifera can be calculated time series of the 13c of calcite precipitated in the late growth stages of planktonic foraminifera from two nearby cores from the caribbean sea result in a better correlation than time series of constant size fractions these 13c records indicate similar 13c values during the last glaciation and the late holocene and a broad deglacial minimum approximately synchronous with a minimum in the 13c records of benthic foraminifera from intermediate depth atlantic cores the deglacial minimum may be a reflection of the isotopic composition of the underlying intermediate water which may be affected by circulation changes or changes in preformed 13c values and or of the flux of water upwelled into the surface layer the small 0 2 to 0 0 glacial interglacial 13c difference in tropical surface water is also believed to be affected by the chemistry of the underlying source water

possible algal origin of long chain odd n alkanes in immature sediments as revealed by distributions and carbon isotope ratios a pliocene oil shale pula hungary a c3 plant triticum aestivum and a c4 plant zea mays were compared using isotopic composition of bulk organic matter along with distributions and individual carbon isotope ratios of n alkanes from organic extracts the microalga botryococcus braunii a race was thus shown to be the main source of the predominant 27 29 and 31 n alkanes of pula sediment therefore the dominance of odd carbon numbered n alkanes in the range c25 35 in extracts from immature sediments shall not be systematically assigned to higher plant contribution but algal input is also possible in fact the long chain n alkanes with an odd predominance previously observed in extracts of various immature sediments are likely to be derived at least partially from algae

loss of carbon from the deep sea since the last glacial maximum deep ocean carbonate ion concentrations co32 and carbon isotopic ratios 13c place important constraints on past redistributions of carbon in the ocean land atmosphere system and hence provide clues to the causes of atmospheric co2 concentration changes however existing deep sea co32 reconstructions conflict with one another complicating paleoceanographic interpretations here we present deep sea co32 for five cores from the three major oceans quantified using benthic foraminiferal boron calcium ratios since the last glacial period combined benthic 13c and co32 results indicate that deep sea released co2 during the early deglacial period 17 5 to 14 5 thousand years ago was preferentially stored in the atmosphere whereas during the late deglacial period 14 to 10 thousand years ago besides contributing to the contemporary atmospheric co2 rise a substantial portion of co2 released from oceans was absorbed by the terrestrial biosphere

carbon isotope constraints on the deglacial co2 rise from ice cores the stable carbon isotope ratio of atmospheric co2 13catm is a key parameter in deciphering past carbon cycle changes here we present 13catm data for the past 24 000 years derived from three independent records from two antarctic ice cores we conclude that a pronounced 0 3 per mil decrease in 13catm during the early deglaciation can be best explained by upwelling of old carbon enriched waters in the southern ocean later in the deglaciation regrowth of the terrestrial biosphere changes in sea surface temperature and ocean circulation governed the 13catm evolution during the last glacial maximum 13catm and atmospheric co2 concentration were essentially constant which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then

what do benthic δ13c and δ18o data tell us about atlantic circulation during heinrich stadial 1 approximately synchronous with the onset of heinrich stadial 1 hs1 13c decreased throughout most of the upper 1000 2500 m atlantic and at some deeper north atlantic sites this early deglacial 13c decrease has been alternatively attributed to a reduced fraction of high 13c north atlantic deep water nadw or to a decrease in the nadw 13c source value here we present new benthic 18o and 13c records from three relatively shallow 1450 1650 m subpolar northeast atlantic cores with published data from other cores these data form a depth transect 1200 3900 m in the subpolar northeast atlantic we compare last glacial maximum lgm and hs1 data from this transect with data from a depth transect of cores from the brazil margin the largest lgm to hs1 decreases in both benthic 13c and 18o occurred in upper waters containing the highest nadw fraction during the lgm we show that the 13c decrease can be explained entirely by a lower nadw 13c source value entirely by a decrease in the proportion of nadw relative to southern ocean water or by a combination of these mechanisms however building on insights from model simulations we hypothesize that reduced ventilation due to a weakened but still active atlantic meridional overturning circulation also contributed to the low 13c values in the upper north atlantic we suggest that the benthic 18o gradients above 2300 m at both core transects indicate the depth to which heat and north atlantic deglacial freshwater had mixed into the subsurface ocean by early hs1

enhanced δ13c and δ18o differences between the south atlantic and south pacific during the last glaciation the deep gateway hypothesis enhanced vertical gradients in benthic foraminiferal 13c and 18o in the atlantic and pacific during the last glaciation have revealed that ocean overturning circulation was characterized by shoaling of north atlantic sourced interior waters nonetheless our understanding of the specific mechanisms driving these glacial isotope patterns remains incomplete here we compare high resolution depth transects of cibicidoides spp 13c and 18o from the southwest pacific and the southwest atlantic to examine relative changes in northern and southern sourced deep waters during the last glacial maximum lgm and deglaciation during the lgm our transects show that water mass properties and boundaries in the south atlantic and pacific were different from one another the atlantic between 1 0 and 2 5 km was more than 1 enriched in 13c relative to the pacific and remained more enriched through the deglaciation during the lgm atlantic 18o was 0 5 more enriched than the pacific particularly below 2 5 km this compositional difference between the deep portions of the basins implies independent deep water sources during the glaciation we attribute these changes to a deep gateway effect whereby northern sourced waters shallower than the drake passage sill were unable to flow southward into the southern ocean because a net meridional geostrophic transport cannot be supported in the absence of a net east west circumpolar pressure gradient above the sill depth we surmise that through the lgm and early deglaciation shoaled northern sourced waters were unable to escape the atlantic and contribute to deep water formation in the southern ocean

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

thermohaline instability in the north atlantic during meltwater events stable isotope and ice rafted detritus records from core so75 26kl portuguese margin a benthic isotope record has been measured for core so75 26kl from the upper portuguese margin 1099 m water depth to monitor the response of thermohaline overturn in the north atlantic during heinrich events evaluating benthic 18o in ts diagrams in conjunction with equilibrium c fractionation implies that advection of mediterranean outflow water mow to the upper portuguese margin was significantly reduced during the last glacial 15 compared to 30 today the benthic isotope record along core so75 26kl therefore primarily monitors variability of glacial north atlantic conveyor circulation the 14c accelerator mass spectrometry ages of 13 54 07 and 20 46 12 ka for two ice rafted detritus ird layers in the upper core section and an interpolated age of 36 1 ka for a third ird layer deeper in the core are in the range of published 14c ages for heinrich events h1 h2 and h4 marked depletion of benthic 13c by 0 7 1 1 during the heinrich events suggests reduced thermohaline overturn in the north atlantic during these events close similarity between meltwater patterns inferred from planktonic 18o at site 609 and ventilation patterns inferred from benthic 13c in core so75 26kl implies coupling between thermohaline overturn and surface forcing as is also suggested by ocean circulation models benthic 13c starts to decrease 1 5 2 5 kyr before heinrich events hl and h4 fully increased values are reached 1 5 3 kyr after the events indicating a successive slowdown of thermohaline circulation well before the events and resumption of the conveyor s full strength well after the events benthic 13c changes in the course of the heinrich events show subtle maxima and minima suggesting oscillatory behavior of thermohaline circulation a distinct feature of thermohaline instability in numerical models inferrred gradual spin up of thermohaline circulation after hl and h4 is in contrast to abrupt wanning in the north atlantic region that is indicated by sudden increases in greenland ice core 18o and in marine faunal records from the northern north atlantic from this we infer that thermohaline circulation can explain only in part the rapid climatic oscillations seen in glacial sections of the greenland ice core record

symmetries in geology and geophysics symmetries have played an important role in a variety of problems in geology and geophysics a large fraction of studies in mineralogy are devoted to the symmetry properties of crystals in this paper however the emphasis will be on scale invariant fractal symmetries the earth s topography is an example of both statistically self similar and self affine fractals landforms are also associated with drainage networks which are statistical fractal trees a universal feature of drainage networks and other growth networks is side branching deterministic space filling networks with side branching symmetries are illustrated it is shown that naturally occurring drainage networks have symmetries similar to diffusion limited aggregation clusters

climate cyclicity in late holocene anoxic marine sediments from the seymour belize inlet complex british columbia abstract an 8 72 m late holocene sediment core vec02a07 obtained from alison sound in the belize seymour inlet complex of central british columbia canada was deposited between 3500 1000 yr bp under primarily anoxic marine conditions this core contains a detailed cyclic record of land sea interactions as evidenced by significant fluctuations in marine primary productivity and changes in the supply of terrigenous material that can be related to long term variation in the relative influence of the aleutian low al and north pacific high nph sedimentologically the core is characterized by alternating intervals of fine grained massive intervals 70 laminated intervals 23 turbidites 5 and graded silt clay layers 2 the laminated intervals are comprised of couplets that vary between light coloured diatom rich layers deposited primarily during the summer months and dark coloured mineral rich layers deposited during winter laminated couplets are most common in portions of the core deposited between 3150 and 2700 yr bp which corresponds to an episode of regional neoglaciation time series analysis was carried out on high resolution particle size measurements obtained from core sub samples and on sediment grey scale colour variability derived from x ray scans of the core non linear time series analyses revealed that the succession of massive and laminated sedimentation displayed characteristics of self organization following a power law relationship for core length segments of 13 cm 50 years of deposition contained evidence of sedimentary depositional cycles of 70 96 135 155 and 250 330 years that reflect changes in al and nph mediated regional precipitation patterns that can in turn be related to larger scale climate drivers such as the pacific decadal oscillation pdo or solar irradiance cyclicity

glacial interglacial circulation changes inferred from 231pa 230th sedimentary record in the north atlantic region 1 studies from the subtropical western and eastern atlantic ocean using the 231pa 230th ratio as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation in this study we present a compilation of existing and new sedimentary 231pa 230th records from north atlantic cores between 1710 and 4550 m water depth comparing sedimentary 231pa 230th from different depths provides new insights into the evolution of the geometry and rate of deep water formation in the north atlantic during the last 20 000 years the 231pa 230th ratio measured in upper holocene sediments indicates slow water renewal above 2500 m and rapid flushing below consistent with our understanding of modern circulation in contrast during the last glacial maximum lgm glacial north atlantic intermediate water gnaiw drove a rapid overturning circulation to a depth of at least 3000 m depth below 4000 m water renewal was much slower than today at the onset of heinrich event 1 transport by the overturning circulation declined at all depths gnaiw shoaled above 3000 m and significantly weakened but did not totally shut down during the bolling allerod ba that followed water renewal rates further decreased above 2000 m but increased below our results suggest for the first time that ocean circulation during that period was quite distinct from the modern circulation mode with a comparatively higher renewal rate above 3000 m and a lower renewal rate below in a pattern similar to the lgm but less accentuated moc during the younger dryas appears very similar to ba down to 2000 m and slightly slower below

north atlantic circulation and reservoir age changes over the past 41 000 years 1 constraints on the timing of atlantic meridional overturning circulation amoc changes during the last deglaciation are fundamental to understanding the climate s rapid response to insolation forcing however uncertainty about high latitude north atlantic hlna radiocarbon reservoir ages has previously precluded robust age model development for this critical region hlna reservoir ages also serve as a proxy for amoc strength we present regionally averaged hlna reservoir ages for 0 to 41 thousand years before the present kyr bp based on over 500 radiocarbon dates from 33 north atlantic cores an early deglacial increase to 1000 14c yr reservoir ages between 18 5 and 16 5 kyr bp suggests reduced amoc before peak heinrich stadial 1 hs1 ice rafted debris ird a rapid decrease in reservoir ages coincident with the ird maximum at 16 kyr bp indicates strong stratification of the upper water column caused by massive freshwater release

does sedimentary 231pa 230th from the bermuda rise monitor past atlantic meridional overturning circulation 1 ocean circulation may have undergone reductions and reinvigorations in the past closely tied to regional climate changes measurements of 231pa 230th ratios in a sediment core from the bermuda rise have been interpreted as evidence that the atlantic meridional overturning circulation amoc was weakened or completely eliminated during a period of catastrophic iceberg discharges heinrich event 1 h1 here we present new data from the bermuda rise that show further 231pa 230th peaks during heinrich 2 h2 and heinrich 3 h3 additionally a tight correlation between diatom abundances biogenic silica and 231pa 230th is discovered in this core our results redirect the interpretation of 231pa 230th from the bermuda rise as a proxy for ocean circulation towards a proxy that reacts highly sensitive to changes of particle composition and water mass properties

intermediate depth warming in the tropical atlantic related to weakened thermohaline circulation combining paleoclimate data and modeling results for the last deglaciation 1 benthic foraminiferal oxygen isotope ratios from two sediment cores recovered at 426 and 1299 m water depth in the eastern and western tropical atlantic show that a slowdown of the thermohaline circulation thc during heinrich event h1 and the younger dryas was accompanied by rapid and intense warming of intermediate depth waters millennial scale covariations of low paleosalinities in the subpolar north atlantic with decreased benthic oxygen isotope ratios in the eastern tropical atlantic throughout the past 10 000 years suggest that thc weakening might be related to middepth warming during the holocene period as well climate model experiments simulating a strong reduction of the thc in the atlantic ocean under present day and glacial conditions reveal that the increase of temperature in the middepth tropical and south atlantic is a common feature for both climatic states caused by a reduced ventilation of cold intermediate and deep waters in conjunction with downward mixing of heat from the thermocline from the similarity of the paleoclimatic records with the model simulations we infer that the characteristic pattern of temperature change in the atlantic ocean related to weakened thermohaline circulation can serve as an indicator of present day and future thc slowdown

calibration of stable isotopic data an enriched δ18o standard used for source gas mixing detection and correction we present empirically based calibrations of our measurements made on a finnigan mat252 equipped with a kiel device to vienna pee dee belemnite using an enriched 18o standard calibrations include corrections for biases caused by the differences in isotopic composition of carbonate standards measured on the two parallel extraction lines of the kiel device and for decreases in the isotopic difference between the reference and sample gas caused by mixing in the source after correcting for these biases the precision of 2200 nbs19 analyses 10 300 g is 0 07 for 18o and 0 03 for 13c we have shared our standard enriched in 18o with 18 laboratories engaged in paleoceanographic research producing the first large scale interlaboratory calibrations for this community using correction procedures reported here water mass reconstructions using data produced on multiple mass spectrometers may now be possible with a precision approaching the level necessary to reconstruct temperature salinity and density variability in the deep ocean

paleonutrient and productivity records from the subarctic north pacific for pleistocene glacial terminations i to v our study addresses fundamental questions of the mode and timing of orbital and millennial scale changes in the meridional overturning circulation moc of the subarctic north pacific particular concerns are the vertical mixing the present and past abundance of nutrients in surface waters despite strong stratification and the north pacific north atlantic seesaw of oscillations in sea surface temperature sst we do this by generating and interpreting multiple records for glacial terminations i v down two long piston cores one each from the western and eastern subarctic pacific chlorins and biogenic opal are proxies for surface water productivity delta 13 c of epibenthic foraminifera is a record of deepwater ventilation and the delta 13 c of n pachyderma sin is a tracer of nutrients in subsurface waters that extend up to the sea surface during times of vertical mixing the degree of mixing is traced by pairing sst and delta 18 o records of planktic surface and subsurface pycnocline dwellers tight age control is deduced from a suite of age calibrated 14 c plateau boundaries for termination i and benthic delta 18 o and geomagnetic events for the last 800 ka carbon 14 paleoreservoir ages record the ages of surface and deep waters to uncover short term changes in moc over termination i we have defined a standard sequence of short term productivity events for termination i also evident during terminations ii to v and subsequent interglacials over the last 450 ka the peak glacial regime of stable stratification and low productivity terminated together with the end of ice rafting and melting near 17 ka similar to 2000 years after the onset of termination i pulses of vertical mixing and incursion of warm surface waters from the subtropics followed convected young water masses finally penetrated down to 3600 m water depth at 17 0 to less than 14 5 ka significantly improving bottom water ventilation through the late deglacial and earliest interglacial mixing with upwelled nutrients from the pycnocline induced short term maxima in algal production of chlorins and biogenic opal near 17 15 and 15 12 ka respectively deglacial meltwater incursions in the aleutian current and silica input from north american rivers also promoted east pacific productivity after 15 5 ka productivity decreased during the late deglacial and early interglacial coeval with an exceptional peak in caco 3 preservation caused by both low organic flux and well ventilated deepwater subsequently low salinity and cool surface waters and in turn stratification were gradually restored a second opal dominated productivity maximum marked the ends of interglacials the deglacial pulses of vertical mixing around 17 11 ka imply an important contribution of the north pacific to the coeval release of oceanic co 2 into the atmosphere and support the east west seesaw model of climate change

self organized complexity in geomorphology observations and models the focus of this paper is to relate fundamental statistical properties of landforms and drainage networks to models that have been developed in statistical physics relevant properties and models are reviewed and a general overview is presented landforms and drainage networks are clearly complex but well defined scaling laws are found coastlines topography contours and lakes are classic self similar fractals the height of topography along a linear track is well approximated as a brownian walk a self affine fractal this type of behavior has also been found in surface physics for example the surface roughness of a fracture an applicable model is the langevin equation the heat equation with a stochastic white noise driver this model also reproduces the statistics of sediment deposition drainage networks were one of the original examples of self similar fractal trees an important advance in quantifying the structure of drainage networks is the application of the tokunaga fractal side branching statistics a classic problem in statistical physics is the diffusion limited aggregation the resulting tree like structures have been shown to also satisfy the tokunaga statistics a modified version of the diffusion limited aggregation model reproduces the statistics of drainage networks it is concluded that the models developed in statistical physics have direct applicability to the fundamental problems in geomorphology

rapid changes in the mechanism of ocean convection during the last glacial period high amplitude rapid climate fluctuations are common features of glacial times the prominent changes in air temperature recorded in the greenland ice cores1 2 are coherent with shifts in the magnitude of the northward heat flux carried by the north atlantic surface ocean3 4 changes in the ocean s thermohaline circulation are a key component in many explanations of this climate flickering5 here we use stable isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate change events deep water was generated more or less continuously in the nordic seas during the latter part of the last glacial period 60 to 10 thousand years ago but by two different mechanisms the deep water formation occurred by convection in the open ocean during warmer periods interstadials but during colder phases stadials a freshening of the surface ocean reduced or stopped open ocean convection and deep water formation was instead driven by brine release during sea ice freezing these shifting magnitudes and modes nested within the overall continuity of deep water formation were probably important for the structuring and rapidity of the prevailing climate changes

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

suborbital intermediate water variability inferred from paired benthic foraminiferal cd ca and δ13c in the tropical west atlantic and linking with north atlantic climates abstract paired benthic cd ca and 13c records have been generated along core m35003 in the western tropical atlantic decreased glacial water column dissolved cadmium cdw and increased benthic 13c indicate enhanced ventilation with nutrient deplete intermediate waters in line with similar inferences from other north atlantic mid depth records an abrupt early deglacial 13c collapse that is associated with a marked positive cdw anomaly indicates a transient collapse of mid depth ventilation from north atlantic sources conceivably in conjunction with the h1 meltwater anomaly the cdw record displays fine scale fluctuations that mimic the greenland dansgaard oeschger d o cycles and show decreased cdw during stadials this pattern is opposite to cdw variations in a deep water record from bermuda rise that display increased cdw concentrations during stadials the divergent pattern between mid depth and deep water cdw records indicates millennial scale switches between deep and shallow convection in the glacial north atlantic at the pace of the d o climatic cycles several high amplitude anomalies occur in the cdw record that reach levels similar to those observed today in the north pacific while a substantial nutrient increase in the mid depth north atlantic cannot be ruled out during these events changes of pore water chemistry and cd p fractionation during biological uptake offer alternative scenarios to explain the peak cdw maxima

refining the stable isotope budget for antarctic bottom water new foraminiferal data from the abyssal southwest atlantic 1 stable isotope tracer budget results suggest the transport to vertical diffusivity ratio for antarctic bottom water aabw in the atlantic was higher at the last glacial maximum lgm reduced mixing across the upper boundary of aabw is consistent with movement of this surface away from the seafloor and may be a factor in sequestering co2 in the abyssal atlantic two key unknowns in the budget are the isotopic composition of aabw and the spatial representativeness of isolated vertical profiles of 18o and 13c due to a lack of core material below 3 km water depth lund et al 2011 based their holocene budget on water column data and their lgm budget on extrapolation of isotopic trends from shallower cores here we determine 18o and 13c for aabw using new isotopic records from 3 to 4 km water depth at the brazil margin the core top data yield tracer budget parameters consistent with water column data in the broader southwest atlantic at the lgm benthic 18o reaches 4 9 at 4 km water depth the highest lgm 18o value in the published literature the corresponding 13c of 0 2 is less depleted than expected and 0 5 greater than 13c in the southeast atlantic our peclet number estimates suggest 13c acted conservatively during both the holocene and lgm both 18o and 13c imply the transport to vertical diffusivity ratio for aabw was an order of magnitude larger during the lgm due to enhanced aabw transport or reduced mixing across its upper boundary

intermediate and deep water mass distribution in the pacific during the last glacial maximum inferred from oxygen and carbon stable isotopes intermediate ocean circulation changes during the last glacial maximum lgm in the north pacifi ch ave been linked with northern hemisphere climate through airesea interactions although the extent and the source of the variability of the processes forcing these changes are still not well resolved the ventilated volumes and ages in the upper wind driven layer are related to the wind stress curl and surface buoyancy fluxes at mid to high latitudes in the north pacific in contrast the deeper thermohaline layers are more effectively ventilated by direct atmosphere sea exchange during convective formation of subantarctic mode waters samw and antarctic intermediate waters aaiw in the southern ocean the precursors of pacific intermediate waters piw in the north pacific results reported here show a fundamental change in the carbon isotopic gradient between intermediate and deep waters during the lgm in the eastern north pacific indicating a deepening of nutrient and carbon rich waters these observations suggest changes in the source and nature of intermediate waters of southern ocean origin that feed piw and enhanced ventilation processes in the north pacific further affecting paleoproductivity and export patters in this basin furthermore oxygen isotopic results indicate these changes may have been accomplished in part by changes in circulation affecting the intermediate depths during the lgm 2010 elsevier ltd all rights reserved

a high resolution record of atmospheric 14c based on hulu cave speleothem h82 abstract the development of a calibration of atmospheric radiocarbon 14c is a significant scientific goal because it provides the means to link the numerous 14c dated paleoclimate records to a common timescale with absolutely dated records and thereby improve our understanding the relationships between the carbon cycle and climate change currently few calibration datasets that directly sample the atmospheric 14c reservoir are available beyond the end of the dendro dated holocene tree ring record at 12 6 kyr bp before 1950 ad in the absence of suitable true atmospheric records 14c calibrations beyond this age limit are based largely on marine data that are complicated by the marine reservoir effect which may have varied over the glacial cycle in this paper we present a high resolution record of u th series and 14c measurements from hulu cave speleothem h82 spanning 10 6 26 8 kyr bp corrections for detrital 230th are negligible and the contribution of 14c free geologic carbon to the speleothem calcite is small 5 6 and is stable across major climate shifts the time series provides a 16 kyr record of atmospheric 14c as well as an updated age model for the existing hulu cave 18o record the 14c data are in good overall agreement with existing marine and terrestrial 14c records but comparisons with the cariaco basin marine 14c record through the deglacial interval reveal that the cariaco reservoir age appears to have varied during parts of the younger dryas and heinrich stadial 1 cold events this highlights the importance of developing extended high resolution marine and terrestrial 14c records as a means of detecting changes in ocean circulation over the glacial cycle

did north atlantic overturning halt 17 000 years ago models indicate that a complete shutdown of deep and intermediate water production is a possible consequence of extreme climate conditions in the northern north atlantic and the high ratio of 231pa to 230th on bermuda rise is evidence that this might have happened 17 ka during heinrich event 1 h1 however new radiocarbon data from bivalves that lived at 4 6 km on the bermuda rise during h1 lead to a different conclusion the bivalve data do indeed indicate ventilation of the deep western north atlantic was suppressed during h1 but not as much as it was during the last glacial maximum we propose that high diatom flux to the bermuda rise during h1 is at least in part responsible for increased 231pa 230th at that time although we cannot say for sure why opal production was so high in a gyre center location at that time increased leakage of silica rich waters from the southern ocean to the north atlantic is one possibility

evidence from the high latitude north atlantic for variations in antarctic intermediate water flow during the last deglaciation we present evidence that the characteristic chemical signature based on coupled benthic foraminiferal cd ca and d13c of antarctic intermediate waters aaiw penetrated throughout the intermediate depths of the atlantic basin to the high latitude north atlantic during the abrupt cooling events of the last deglaciation heinrich 1 and the younger dryas aaiw may play the dynamic counterpart to the bipolar seesaw when near freezing salty bottom waters from the antarctic aabw sluggishly ventilate the deep ocean our data reinforce the concept that interglacial circulation is stabilized by salinity feedbacks between salty northern sourced deep waters nadw and fresh southern sourced waters aabw and aaiw further the glacial ocean may be susceptible to the more finely balanced relative densities of nadw and aaiw due to either freshwater input or a reversal of the salinity gradient such that the ocean is poised for nadw collapse via a negative salinity feedback the unstable climate of the glacial period and its termination may arise from the closer competition for ubiquity at intermediate depths between northern and southern sourced intermediate waters

increased ventilation age of the deep northeast pacific ocean during the last deglaciation the amount of radiocarbon depleted carbon dioxide in the atmosphere rose dramatically during the last deglaciation estimates of the radiocarbon content of water at 2 7 km depth in the northeast pacific ocean over the past 24 000 years suggest that this water mass was not a significant source of this carbon

quantifying a potential bias in probabilistic seismic hazard assessment seismotectonic zonation with fractal properties the accurate definition and characterization of relevant seismic sources are critical steps in probabilistic seismic hazard assessment psha this is particu larly challenging in low seismicity regions because observation periods are relatively short seismicity is often diffuse and active faults are difficult to identify in such regions seismogenic sources are typically represented as areal sources zones with equal seismic potential however observed seismicity is never truly uniformly dis tributed but clusters at all scales a reflection of the seismotectonic forces and tectonic structures in this study we use a fractal scaling approach to explore a more realistic characterization of the seismicity distribution within each source zone for a hypothe tical square source zone we compute hazard curves and hazard maps resulting from simulations of uniformly distributed seismicity fractal dimension d 2 0 and we compare these with those resulting from simulations of clustered seismicity 1 0 d 2 0 we find that the assumption of uniform distribution of events leads systematically to a higher estimate of hazard within the source zone this overestima tion is increasing for lower probability levels equally important the assumed uniform distribution underestimates the uncertainty of the hazard by up to a factor of three we perform an extensive sensitivity study of psha input parameters illustrating the complexity of the interaction between the specific setup and the resulting impact on the psha we apply the fractal scaling approach to the seismicity of switzerland and measure the fractal dimension of instrumental seismicity for the past 30 yr d 1 5 using this value for synthetic catalogs we build a fractal seismic zonation and hazard model we find that in general the assumption of uniform distribution of events over estimates the mean hazard in switzerland by 3 to 20 and the uncertainty distribu tion estimation is 50 to 100 narrower than in fractal distribution depending on the location and the probability level of interest

freshwater input and abrupt deglacial climate change in the north atlantic greenland ice core records indicate that the last deglaciation 7 21 ka was punctuated by numerous abrupt climate reversals involving temperature changes of up to 5 10oc within decades however the cause behind many of these events is uncertain a likely candidate may have been the input of deglacial meltwater from the laurentide ice sheet lis to the high latitude north atlantic which disrupted ocean circulation and triggered cooling yet the direct evidence of meltwater input for many of these event has so far remained undetected in this study we use the geochemistry paired mg ca 18 o of planktonic foraminifera from a sediment core south of iceland to reconstruct the input of freshwater to the northern north atlantic during abrupt deglacial climate change our record can be placed on the same timescale as ice cores and therefore provides a direct comparison between the timing of freshwater input and climate variability meltwater events coincide with the onset of numerous cold intervals including the older dryas 14 0 ka two events during the allerod at 13 1 and 13 6 ka the younger dryas 12 9 ka and the 8 2 ka event supporting a causal link between these abrupt climate changes and meltwater input during the bolling allerod warm interval we find that periods of warming are associated with an increased meltwater flux to the northern north atlantic which in turn induces abrupt cooling a cessation in meltwater input and eventual climate recovery this implies that feedback between climate and meltwater input produced a highly variable climate a comparison to published data sets suggests that this feedback likely included fluctuations in the southern margin of the lis causing rerouting of lis meltwater between southern and eastern drainage outlets as proposed by clark et al science 2001 v293 283 287

high resolution evidence for linkages between nw european ice sheet instability and atlantic meridional overturning circulation published studies show that ice rafted debris ird deposition preceding heinrich h events h1 and h2 in the ne atlantic was derived from the nw european ice sheets nweis possibly offering clues about ice sheet sensitivity and stability and the mechanisms that caused periodic collapse of the laurentide ice sheet lis we present detailed lithological and geochemical records including radiogenic isotope fingerprinting of ird deposits from core md01 2461 proximal to the last glacial british ice sheet bis demonstrating persistent instability of the bis with significant destabilisation occurring 1 5 1 9 kyr prior to both h1 and h2 dated at 16 9 and 24 1 kyr bp respectively in the ne atlantic paired mg ca and 18o data from the surface dwelling globigerina bulloides and subsurface dwelling neogloboquadrina pachyderma sinistral are used to determine late glacial variability of temperature salinity and stratification of the upper water column a picture emerges that the bis was in a continuing state of readjustment and never fully reached steady state increased sea surface temperatures appear to have triggered the episode of nweis instability preceding h1 it seems most probable that the so called precursor events were not linked to the h events however if response to a common thermal forcing is considered an increased response time of the lis up to 2 kyr longer than the nweis may be inferred negative salinity excursions of up to 2 6 indicate significant incursions of melt water associated with peaks in nweis instability decreased surface density led to a more stable stratification of the upper water column and is associated with reduced ventilation of intermediate waters recorded in depleted epibenthic 13c cibicidoides wuellerstorfi we suggest that instability and meltwater forcing of the nweis temporarily weakened atlantic meridional overturning circulation allowing transient advance of southern sourced waters to this site prior to h events 1 and 2

changes in the distribution of δ13c of deep water σco2 between the last glaciation and the holocene carbon isotopic measurements on the benthic foraminiferal genus cibicidoides document that mean deep ocean 13c values were 0 46 lower during the last glacial maximum than during the late holocene the geographic distribution of 13c was altered by changes in the production rate of nutrient depleted deep water in the north atlantic during the late holocene north atlantic deep water with high 13c values and low nutrient values can be found throughout the atlantic ocean and its effects can be traced into the southern ocean where it mixes with recirculated pacific deep water during the glaciation decreased production of north atlantic deep water allowed southern ocean deep water to penetrate farther into the north atlantic and across low latitude fracture zones into the eastern atlantic mean southern ocean 13c values during the glaciation are lower than both north atlantic and pacific 13c values suggesting that production of nutrient depleted water occurred in both oceans during the glaciation enriched 13c values in shallow cores within the atlantic ocean indicate the existence of a nutrient depleted water mass above 2000 m in this ocean

evidence for substantial accumulation rate variability in antarctica during the holocene through synchronization of co 2 in the taylor dome dome c and dml ice cores high resolution records of atmospheric co2 concentration during the holocene are obtained from the dome concordia and dronning maud land antarctica ice cores these records confirm that the co2 concentration varied between 260 and 280 ppmv in the holocene as measured in the taylor dome ice core however there are differences in the co2 records most likely caused by mismatches in timescales matching the taylor dome timescale to the dome c timescale by synchronization of co2 indicates that the accumulation rate at taylor dome increased through the holocene by a factor two and bears little resemblance to the stable isotope record used as a proxy for temperature this result shows that different locations experienced substantially different accumulation changes and casts doubt on the often used assumption that accumulation rate scales with the saturation vapor pressure as a function of temperature at least for coastal locations d 2004 elsevier b v all rights reserved

calibrations for benthic foraminiferal mg ca paleothermometry and the carbonate ion hypothesis benthic foraminiferal magnesium calcium ratios were determined on one hundred and forty core top samples from the atlantic ocean the norwegian sea the indian ocean the arabian sea and the pacific ocean mostly at sites with bottom water temperatures below 5 c mg ca ratios are consistently lower by not vert similar 0 2 mmol mol in samples cleaned using oxidative and reductive steps than using oxidative cleaning differences between cibicidoides species have been identified mg ca of cibicidoides robertsonianus cibicidoides kullenbergi cibicidoides wuellerstorfi comparison with bottom water temperatures support observations of lowered mg ca of c wuellerstorfi at temperature below not vert similar 3 c compared with values predicted by published calibrations and from other cibicidoides species hydrographic data shows that carbonate ion saturation co32 decreases rapidly below this temperature an empirical sensitivity of co32 on mg ca has been established for c wuellerstorfi of 0 0086 0 0006 mmol mol mol kg a novel application using modern temperatures and last glacial maximum temperatures derived via pore fluid modelling supports a carbonate ion saturation state effect on mg incorporation this may significantly affect calculated 18oseawater obtained from foraminiferal 18o and mg ca temperature

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

rapid sea level fall and deep ocean temperature change since the last interglacial period we have dated huon peninsula papua new guinea and barbados corals that formed at times since the last interglacial period applying both 230 th and 231 pa dating techniques as a test of age accuracy we show that marine isotope stage mis 5e ended prior to 113 1 8 0 7 kyr when sea level was 319 m during mis 5b sea level was 357 m at 92 6 8 0 5 kyr having dropped about 40 m in approximately 10 kyr during the mis 5c 5b transition sea level then rose more than 40 m during the mis 5b 5a transition also in about 10 kyr mis 5a lasted until at least 76 2 8 0 4 kyr at a level of 324 m at that time combined with earlier data that places mis 4 sea level at 381 m at 70 8 kyr our late mis 5a data indicate that sea level fell almost 60 m in less than 6 kyr 10 6 m kyr during the mis 5 4 transition the magnitude of the drop is half that of the glacial interglacial amplitude and approximatelyequivalent to the volume of the present dayantarctic ice sheet during this interval the minimum average rate of net continental ice accumulation was 18 cm yr likely facilitated by efficient moisture transport from lower latitudes at three specific times 60 6 8 0 3 50 8 8 0 3 and 36 8 0 2 kyr during mis 3 sea level was between 385 and 374 m sea level then dropped to 3107 m at 23 7 8 0 1 kyr early in mis 2 before dropping further to last glacial maximum lgm values and then rising to present values during the last deglaciation times of rapid sea level drop correspond to times of high winter insolation at low northern latitudes and high winter latitudinal gradients in northern hemisphere insolation supporting the idea that these factors mayhave resulted in high water vapor pressure in moisture sources and efficient moisture transport to high latitude glaciers therebycontributing to glacial buildup we combined our sea level results with deep sea n 18 o records as a means of estimating the temperature and ice volume components in the marine n 18 o record this analysis confirms large deep ocean temperature shifts following mis 5e and during termination i deep ocean temperatures changed bymuch smaller amounts between mis 5c and 2 maximum temperature shift in the deep pacific is about 2 whereas the shift at a site in the atlantic is 4 under glacial conditions temperatures at both sites are near the freezing point the shift in the atlantic is likelycaused bya combination of changing proportions of northern and southern source waters as well as changing temperature at the sites where these deep waters form

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

radiocarbon variability in the western north atlantic during the last deglaciation we present a detailed history of glacial to holocene radiocarbon in the deep western north atlantic from deep sea corals and paired benthic planktonic foraminifera the deglaciation is marked by switches between radiocarbon enriched and depleted waters leading to large radiocarbon gradients in the water column these changes played an important role in modulating atmospheric radiocarbon the deep ocean record supports the notion of a bipolar seesaw with increased northern source deep water formation linked to northern hemisphere warming and the reverse in contrast the more frequent radiocarbon variations in the intermediate deep ocean are associated with roughly synchronous changes at the poles

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

glacial water mass structure and rapid δ18o and δ13c changes during the last glacial termination in the southwest pacific abstract changes in ocean circulation are thought to have contributed to lowering glacial atmospheric co 2 levels by enhancing deep ocean sequestration of carbon that was returned to the atmosphere during glacial terminations high resolution benthic foraminiferal 13 c and 18 o records from a depth transect of cores in the southwest pacific ocean presented here provide evidence that both wind and thermohaline driven circulation drove co 2 from the ocean during the last deglaciation shallow geochemical stratification in the glacial southern ocean was followed by a short pulse of rapid 13 c enrichment to intermediate water depths during heinrich stadial 1 indicative of better ventilated intermediate waters co occurring with documented wind driven upwelling in the southern ocean intermediate depth 13 c enrichment paused at the start of the antarctic cold reversal 14 7 ka implying a brief shallow restratification while deeper layers were progressively flushed of 13 c depleted and 18 o enriched waters likely caused by the increasing influence of deep waters sourced from the north atlantic the coincidence of atmospheric co 2 increases with these geochemical shifts in both shallow and deep cores suggests that shifts in both atmospheric and oceanic circulation contributed to the deglacial rise of co 2