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

application of stochastic simulation to co2 flux from soil mapping and quantification of gas release 1 conditional sequential gaussian simulations sgs have been applied for the first time to the study of soil diffuse degassing from different volcanic and nonvolcanic systems the application regards five data sets of soil co2 fluxes measured with the accumulation chamber methodology at the volcanic areas of solfatara of pozzuoli italy vesuvio cone italy nisyros greece and horseshoe lake california and at the nonvolcanic degassing area of poggio dell olivo italy the sgs algorithm was used to generate 100 realizations of co2 flux for each area probabilistic summaries of these simulations together with the information given by probability plots were used 1 to draw maps of the probability that co2 fluxes exceed thresholds specific for a background flux i e to define the probable extension of the degassing structures 2 to calculate the total co2 output and 3 to quantify the uncertainty of the estimation the results show that the sgs is a suitable tool to model soil diffuse degassing producing realistic images of the distribution of the co2 fluxes that honor the histogram and variogram of the original data moreover the relation between the sample design and the uncertainty of estimation was investigated leading to an empirical relation between uncertainty and the sampling density that can be useful for the planning of future co2 flux surveys

north atlantic versus southern ocean contributions to a deglacial surge in deep ocean ventilation past glacial interglacial climate transitions were accompanied by millennial scale pulses in atmospheric co2 that are widely thought to have resulted from the release of co2 via the southern ocean however direct proxy evidence for a southern ocean role in regulating past ocean atmosphere co2 exchange is scarce here we use combined radiocarbon and neodymium isotope measurements from the last deglaciation to confirm greatly enhanced overturning and or air sea exchange rates relative to today in particular during the bolling allerod warm interval we show that this deglacial pulse in ocean ventilation was not driven by the north atlantic overturning alone and must have involved an increase in the ventilation of southern sourced deep waters our results thus confirm the removal of a physical and or dynamical barrier to effective air sea co2 exchange in the southern ocean during deglaciation and highlight the antarctic region as a key locus for global climate carbon cycle feedbacks

the hafnium and neodymium isotope composition of seawater in the atlantic sector of the southern ocean we present the first combined dissolved hafnium hf and neodymium nd concentrations and isotope compositions of deep water masses from the atlantic sector of the southern ocean eight full depth profiles were analyzed for hf and twelve for nd hafnium concentrations are generally depleted in the upper few hundred meters ranging between 0 2 pmol kg and 0 4 pmol kg and increase to relatively constant values of around 0 6 pmol kg in the deeper water column at the stations north of the polar front pf nd concentrations increase linearly from about 10 pmol kg at depths of 200 m to up to 31 pmol kg close to the bottom indicating particle scavenging and release within the weddell gyre wg however nd concentrations are essentially constant at 25 pmol kg at depths greater than 1000 m the distributions of both elements show a positive correlation with dissolved silicon implying a close linkage to diatom biogeochemistry hafnium essentially shows invariant isotope compositions with values averaging at ehf 4 6 whereas nd isotopes mark distinct differences between water masses such as modified north atlantic deep water nadw end 11 to 10 and antarctic bottom water aabw end 8 6 to 9 6 but also waters locally advected via the agulhas current can be identified by their unradiogenic nd isotope compositions mixing calculations suggest that a small fraction of nd is removed by particle scavenging during mixing of water masses north of the pf nevertheless the nd isotope composition has apparently not been significantly affected by uptake and release of nd from particles as indicated by mixing calculations a mixing envelope of an approximated north pacific and a north atlantic end member shows that nd isotope and concentration patterns in the lower circumpolar deep water lcdw can be fully explained by 30 70 percentage contributions of these respective end members

synchronous and proportional deglacial changes in atlantic meridional overturning and northeast brazilian precipitation changes in heat transport associated with fluctuations in the strength of the atlantic meridional overturning circulation amoc are widely considered to affect the position of the intertropical convergence zone itcz but the temporal immediacy of this teleconnection has to date not been resolved based on a high resolution marine sediment sequence over the last deglaciation we provide evidence for a synchronous and near linear link between changes in the atlantic interhemispheric sea surface temperature difference and continental precipitation over northeast brazil the tight coupling between amoc strength sea surface temperature difference and precipitation changes over northeast brazil unambiguously points to a rapid and proportional adjustment of the itcz location to past changes in the atlantic meridional heat transport

hindered settling of sand grains the sedimentation rate of sand grains in the hindered settling regime has been considered to assess particle shape effects the behaviour of various particulate systems involving sand has been compared with the widely used richardson zaki expression the general form of the expression is found to hold in as much as remaining as a suitable means to describe the hindered settling of irregular particles the sedimentation exponent n in the richardson zaki expression is found to be significantly larger for natural sand grains than for regular particles the hindered settling effect is therefore greater leading to lower concentration gradients than expected the effect becomes more pronounced with increasing particle irregularity at concentrations around 0 4 the hindered settling velocity of fine and medium natural sands reduces to about 70 of the value predicted using existing empirical expressions for n using appropriate expressions for the fluidization velocity and the clear water settling velocity a simple method is discussed to evaluate the sedimentation exponent and to determine the hindered settling effect for sands of various shapes

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

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

synchronous deglacial overturning and water mass source changes understanding changes in ocean circulation during the last deglaciation is crucial to unraveling the dynamics of glacial interglacial and millennial climate shifts we used neodymium isotope measurements on postdepositional iron manganese oxide coatings precipitated on planktonic foraminifera to reconstruct changes in the bottom water source of the deep western north atlantic at the bermuda rise comparison of our deep water source record with overturning strength proxies shows that both the deep water mass source and the overturning rate shifted rapidly and synchronously during the last deglacial transition in contrast any freshwater perturbation caused by heinrich event 1 could have only affected shallow overturning these findings show how changes in upper ocean overturning associated with millennial scale events differ from those associated with whole ocean deglacial climate events

volatiles and energy released by purace volcano total co2 output of purace volcano colombia was estimated on the basis of fluids discharged by fumaroles soil gases and dissolved carbon species in the aquifer the soil co2 emission was computed from a field survey of 512 points of co2 soil flux measurements at the main degassing areas of purace volcano the co2 flux from purace s plume was estimated using an indirect method that used the so2 plume flux and co2 so2 ratio of the main high temperature fumarole the total output of co2 was estimated at 1500 t day the main contribution of co2 comes from the plume summit degassing and from soil degassing that emit 673 and 812 t day respectively the contributions of summit and soil degassing areas are comparable indicating an intermediate degassing style partitioned between closed and open conduit systems the estimated water vapor discharge as derived from the chemical composition of the fumaroles the h2o co2 ratio and the so2 plume flux allowed calculation of the total thermal energy fumarolic soil degassing and aquifer released from the purace volcanic system this was 360 mw

high resolution stratigraphy in late pleistocene holocene sediments of the vema channel abstract twenty five giant gravity cores ggc were obtained from the southwest flank of the rio grande rise in the summer of 1980 and were analyzed for time slice interpretations of the late pleistocene paleoceanography of the southwestern atlantic the cores span a depth interval of 1430 4148 m encompassing each of the principal deep water masses the suite of cores contains a continuous depositional record of the past 150 000 200 000 years from calcium carbonate oxygen isotope carbon 14 and biostratigraphic analyses it is possible to determine the precision in core to core correlation which is obtainable within this region of relatively low accumulation rates 0 5 2 0 cm 10 3 yrs calcium carbonate analyses were performed on each of the 25 cores at 1 cm sampling intervals using a technique that yields an analytical precision of 0 25 the carbonate curves show glacial interglacial amplitudes of typically 10 30 caco3 higher frequency amplitudes of 2 5 are also present both the glacial interglacial and the higher frequency carbonate signals can be correlated from core to core over the entire depth interval of the transect and are essentially synchronous based on independent stratigraphic control provided in selected cores by 18o 14c and biostratigraphic analyses despite the low sedimentation rates within this particular region we obtain a precision in core to core correlation of 1000 2000 yrs over the late pleistocene holocene these high resolution studies from the vema channel have important implications for interpreting the effects of bioturbation on a given stratigraphic sequence modeling the effects of bioturbation on the abundance and isotopic records of the benthonic foraminifera planulina wuellerstorfi suggests that for the region of the vema channel rio grande rise invalid stratigraphic and paleoceanographic interpretations may result if abundance variations in this species are ignored the results of these analyses show that it is possible to generate detailed stratigraphies in regions that have not previously been selected for high resolution studies solely because of relatively low accumulation rates of sediments our results indicate that carbonate analyses in some regions may provide a distinct advantage over 18o analyses because of the ease of analysis and high precision for identifying low amplitude high frequency fluctuations which can be correlated from core to core at the same time independent stratigraphic control via 18o or 14c is essential to verify whether this technique of carbonate curve matching is valid

deep water provenance and dynamics of the de glacial atlantic meridional overturning circulation abstract reconstructing past modes of ocean circulation is an essential task in paleoclimatology and paleoceanography to this end we combine two sedimentary proxies nd isotopes e nd and the 231pa 230th ratio both of which are not directly involved in the global carbon cycle but allow the reconstruction of water mass provenance and provide information about the past strength of overturning circulation respectively in this study combined 231pa 230th and e nd down core profiles from six atlantic ocean sediment cores are presented the data set is complemented by the two available combined data sets from the literature from this we derive a comprehensive picture of spatial and temporal patterns and the dynamic changes of the atlantic meridional overturning circulation over the past 25 ka our results provide evidence for a consistent pattern of glacial stadial advances of southern sourced water along with a northward circulation mode for all cores in the deeper 3000 m atlantic results from shallower core sites support an active overturning cell of shoaled northern sourced water during the lgm and the subsequent deglaciation furthermore we report evidence for a short lived period of intensified amoc in the early holocene

diffuse co2 emission rate from pululahua and the lake filled cuicocha calderas ecuador abstract we report herein the first results of two soil co 2 efflux surveys carried out at cuicocha lake filled and pululahua caldera volcanic systems ecuador a total of 172 and 217 soil co 2 efflux measurements were taken at the surface environment of pululahua and cuicocha calderas respectively by means of the accumulation chamber method during the summer of 2006 to constrain the total co 2 output from the studied area soil co 2 efflux values ranged from non detectable up to 48 5 and 141 7 g m 2 d 1 for cuicocha and pululahua calderas respectively in addition probability graphs were used to distinguish the existence of different geochemical populations sequential gaussian simulation was used to construct an average map for 100 simulations and to compute the total co 2 emission at each studied area 106 and 270 t d 1 metric tons per day for cuicocha 13 3 km 2 and pululahua 27 6 km 2 volcanoes respectively

reactivity of neodymium carriers in deep sea sediments implications for boundary exchange and paleoceanography the dissolved neodymium nd isotopic distribution in the deep oceans is determined by continental weathering inputs water mass advection and boundary exchange between particulate and dissolved fractions reconstructions of past nd isotopic variability may therefore provide evidence on temporal changes in continental weathering inputs and or ocean circulation patterns over a range of timescales however such an approach is limited by uncertainty in the mechanisms and importance of the boundary exchange process and the challenge in reliably recovering past seawater nd isotopic composition end from deep sea sediments this study addresses these questions by investigating the processes involved in particulate solution interactions and their impact on nd isotopes a better understanding of boundary exchange also has wider implications for the oceanic cycling and budgets of other particle reactive elements sequential acid reductive leaching experiments at ph 2 5 on deep sea sediments from the western indian ocean enable us to investigate natural boundary exchange processes over a timescale appropriate to laboratory experiments we provide evidence that both the dissolution of solid phases and exchange processes influence the end of leachates which suggests that both processes may contribute to boundary exchange we use major element and rare earth element ree data to investigate the pools of nd that are accessed and demonstrate that sediment leachate end values cannot always be explained by admixture between an authigenic component and the bulk detrital component for example in core wind 24b acid reductive leaching generates end values between 11 and 6 as a function of solution solid ratios and leaching times whereas the authigenic components have end 11 and the bulk detrital component has end 15 we infer that leaching in the mascarene basin accesses authigenic components and a minor radiogenic volcanic component that is more reactive than madagascan derived clays the preferential mobilisation of such a minor component demonstrates that the nd released by boundary exchange could often have a significantly different end composition than the bulk detrital sediment these experiments further demonstrate certain limitations on the use of acid reductive leaching to extract the end composition of the authigenic fraction of bulk deep sea sediments for example the detrital component may contain a reactive fraction which is also acid extractible while the incongruent nature of this dissolution suggests that it is often inappropriate to use the bulk detrital sediment elemental chemistry and or end composition when assessing possible detrital contamination of leachates based on the highly systematic controls observed and evidence from ree patterns on the phases extracted we suggest two approaches that lead to the most reliable extraction of the authigenic end component and good agreement with foraminiferal based approaches either i leaching of sediments without a prior decarbonation step or ii the use of short leaching times and low solution solid ratios throughout

water mass gradients of the mid depth southwest atlantic during the past 25 000 years abstract antarctic intermediate water aaiw plays a central role in the atlantic meridional overturning circulation amoc as the return flow of northern sourced water nsw and is therefore of significant importance for the global climate past variations of the boundary between aaiw and nsw have been extensively investigated yet available results documenting the prevailing depth of this boundary and the southern extent of nsw during the last ice age remain ambiguous here we present five new timeseries focusing on the authigenic neodymium isotope signal in sediment cores retrieved from the southwest atlantic covering the past 25 000 years the sites are situated along the southern brazil margin and form a bathymetric transect ranging between 1000 and 3000 m water depth encompassing the modern water mass boundaries of aaiw and nsw and therefore allow their reconstruction since the last glacial maximum lgm the new nd isotope records show little change between the lgm and early deglaciation as well as relatively homogeneous values over the full depth range of the cores during these times these results strongly contrast with epibenthic foraminiferal stable carbon isotope records 13 c from the same sites which exhibit highest glacial values at mid depths presumably related to nsw mixing into southern sourced water we propose that the discrepancy between these two independent water mass proxies is partly related to changes in nd end member properties of glacial aaiw the combination of elevated glacial dust fluxes and as a result sustained export productivity caused high sinking particle flux in the western south atlantic where aaiw is forming higher particle flux would have increased the removal scavenging of nd from shallow waters thus reducing the nd concentration and overprinting the isotopic signature of the glacial aaiw end member only under consideration of changes in nd end member properties along with non conservative processes such as remineralization of organic matter influencing past seawater 13 c can we reconcile the water mass reconstructions from both proxies

comagmatic granophyre and dacite from karymsky volcanic center kamchatka experimental constraints for magma storage conditions abstract despite a 30 000 years difference in age two caldera forming eruptions at karymsky volcanic center kamchatka karymsky 7900 yr bp and academy nauk ca 40 000 yr bp produced two pyroxene dacites with the same composition and mineralogy granophyric xenoliths of the identical whole rock chemistry were found in basalts erupted within academy nauk caldera in 1996 unlike the dacites however the granophyres are holo crystalline and contain biotite and amphibole large amphibole phenocrysts contain rare inclusions of clinopyroxenes which compositionally overlap with clinopyroxenes in the dacites the al content of the amphibole suggests it grew at a pressure of about 100 mpa results of hydrothermal experiments and petrologic observations indicate that academy nauk and karymsky dacites were last equilibrated at 883 19 c 100 15 mpa and 871 19 c 85 18 mpa respectively both at water saturated conditions the mineral assemblage of granophyre is reproduced by isobaric crystallization of the dacite at 100 mpa implying that the granophyres were sampled from the crystallized silicic reservoir that produced the caldera forming eruption of academy nauk similar chemical compositions of karymsky and academy nauk dacites indicate that both were derived from the same crustal level source the eruptive history of the calderas can best be explained by two 10 12 km 3 dacitic batches that detached from a parental body situated in the lower crust then ascended to 3 4 km depth re equilibrated and erupted

neodymium isotopes and concentrations in caribbean seawater tracing water mass mixing and continental input in a semi enclosed ocean basin we present the first full water column nd isotope end and concentration data for caribbean seawater as well as for stations close to the orinoco river mouth and in the florida straits the surface inflow into the southeastern caribbean via the guyana current is characterized by an endsignature of 10 9 which is a consequence of the mixing of relatively unradiogenic endsignatures 13 6 supplied by the orinoco river with contributions from the amazon river 10 despite the proximity to land sub surface and intermediate waters within the caribbean largely retain the endsignatures of their source water masses in the atlantic in contrast the deep waters of the caribbean show endsignatures at least 3 endunits more radiogenic than the inflowing upper north atlantic deep water unadw a endshift from 13 to 9 7 can be explained by addition of radiogenic nd to the deep caribbean through weathering inputs from land however in order to balance such large shifts in endwith at the same time modest increases in nd concentrations nd must also be removed from seawater within the basin it is suggested that the long residence time of deep waters in the caribbean allows significant interaction of seawater with sinking particles and seafloor sediments resulting in more radiogenic values these findings have implications for the use of endas a proxy for paleocirculation in restricted basins in which the residence times of the deep waters are long

carbon dioxide emissions from specchio di venere pantelleria italy we have mapped the diffuse co2 efflux from the specchio di venere lake area using the accumulation chamber method we calculated a co2 emission of 43 5 t day 1 for the area studied accounting for both diffuse degassing from soil and bubbling through the lake we also present data on the water composition of specchio di venere lake the polla 3 spring and liuzza well on the basis of water chemistry two physical chemical processes evaporation and mineral precipitation of carbonate species are invoked to explain the co2 degassing for the lake area

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

neodymium isotopic evidence for linked changes in southeast atlantic and southwest pacific circulation over the last 200 kyr knowledge of the geometry and strength of the deep overturning circulation is central to the understanding of past climate variability on glacial interglacial g i timescales in this study neodymium nd isotopic ratios on planktonic foraminifera are used to reconstruct the water mass source and mixing history of intermediate and deep water in the southeast se atlantic and southwest sw pacific over the past 200 kyr from five sediment cores nd isotopes from a depth transect of cores in the se atlantic displayed a stronger geochemical gradient around 3 5 km at the lgm with higher end values of 6 0 below that boundary than those of 7 8 above in contrast a similar end value 9 5 is observed at both the intermediate and abyssal depths in the holocene the glacial upper ocean is 1 8 end units less radiogenic than the lower ocean reflecting an increase in the amount of north atlantic component water nacw in the upper se atlantic a coherent nd isotope change was observed in the se atlantic and sw pacific intermediate and deep water with major excursion to more radiogenic end values during marine isotope stage mis 2 4 and 6 this suggests the flux of nacw to the southern ocean was reduced during cold marine stages possibly accompanied by changes in the water mass geometry the constant 2 end unit offset between intermediate water in the se atlantic and sw pacific suggests the persistent propagation of less radiogenic nacw to the upper pacific ocean over the last glacial cycle moreover the larger glacial vertical end gradients between the intermediate and deep waters in both the se atlantic and sw pacific indicate a decreased proportion of nacw entrainment into the deep oceans consistent with studies proposing reduced mixing between the upper and lower meridional overturning cells

the 1996 eruption of karymsky volcano kamchatka historical record of basaltic replenishment of an andesite reservoir the simultaneous eruption in 1996 of andesite from karymsky volcano and of basalt from the academy nauk vent 6km away appears to provide a case of mafic recharge of an andesite reservoir for which the time of recharge is exactly known and direct samples of the recharging magma are available the explosive phreato magmatic eruption of basalt was terminated in less than 24h whereas andesite erupted continuously during the following 4 years detailed petrological study of volcanic ash bombs and lavas of karymsky andesite erupted during the period 1996 1999 provides evidence for basaltic replenishment at the beginning of the eruptive cycle as well as a record of compositional variations within the karymsky magma reservoir induced by basaltic recharge shortly after the beginning of the eruption the composition of the matrix glass of the karymsky tephra became more mafic and then within 2 months gradually returned to its original state and remained almost constant for the following 3 years further evidence for basaltic replenishment is provided by the presence of xenocrysts of basaltic origin in the andesite of karymsky a conspicuous portion of the plagioclase phenocrysts in the karymsky andesite has calcic cores with compositions and textures resembling those of plagioclases in the academy nauk basalt similarly the earlier portion of the andesite of the eruption sequence contains rare olivines which occur as resorbed cores in pyroxenes the composition of the olivine matches that of olivines in the academy nauk basalt the sequence of events appears to be 1 injection of basaltic magma into the karymsky chamber with immediate compensating expulsion of pre existing chamber magma from the karymsky central vent 2 direct mixing of basaltic and andesitic magmas with dispersal of phenocrysts associated with the basalt throughout the andesite so that newly mixed magma appeared at the vent within 2 months 3 re establishment of thermal and chemical equilibrium within the reservoir involving crystallization in the new hybrid liquid which returned the melt composition to normal formed rims on inherited calcic plagioclase and caused the resorption of dispersed olivine xenocrysts taken together these findings indicate that the karymsky magma reservoir was recharged by basalt at the onset of the 1996 eruptive cycle the rapidity and thoroughness of mixing of the basalt with the preexisting andesite probably reflects the modest contrast in temperature viscosity and density between the two magmas

posteruption chemical evolution of a volcanic caldera lake karymsky lake kamchatka 1 the 1996 short lived subaqueous eruption at the karymsky caldera lake suddenly changed the composition of the lake water the lake with a surface area of 10 km2 and a volume of 0 5 km3 became acidic increased its salinity to 1000 mg kg and became dominated by so42 and ca2 since the eruption the lake chemistry has evolved in a predictable manner described by simple box model as a result of dilution by incoming so4 ca mg poor water so4 ca and mg concentrations follow a simple exponential decrease with a characteristic time close to the residence time of the lake na k and cl decrease relatively significantly slower indicating a continuing input of these constituents into the lake that was initiated during the eruption thus the dynamics of two groups of lake water solutes can be predicted by a simple box model for water and solute mass balance

co2 flux and chemistry of el chichon crater lake mexico in the period 2013 2015 evidence for the enhanced volcano activity the co2 flux from el chichon crater in the period from 2014 to 2015 increased by a factor of 3 from 260 t d 1 to 800 t d 1 compared to the 2007 2008 data the mechanism triggering the co2 flux from the lake surface has changed from being dominantly diffusive to mainly advective bubbling the cl concentration was steadily decreasing during the last two decades in the na cl boiling springs feeding the lake since 2013 for both lake and sp springs the cl concentration has increased up to the 2005 cl concentration levels a large degassing spot in the middle of the lake was found in april 2015 with a co2 flux of more than 10 000 g m 2 d 1 these observations are the evidence of the onset of a new stage of activity within the volcano hydrothermal system of el chichon volcano associated most probably with changes in the magmatic activity at depth

terminal settling velocity of commonly occurring sand grains published measurements of terminal settling velocity for commonly occurring sands are used to develop three equations which join into a single segmented curve of dimensionless form results are noticeably different from those for spheres of similar diameter and permit calculation of the settling velocity for usual sand grains without specification of exact grain shape for quartz in water the three equations of different settling regimes correspond approximately to very fine sand fine to coarse sand and very coarse sand

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

hindered bedload settling as a model of sand bed planation by water waves the interrelationships between fluid flows and the surface forms of underlying movable beds are crucial in interpreting sedimentary structures and in predicting hydraulic drag energetic flows can erode all features from a sediment bed and transition to such a planar bed is important to the processes of sediment transport by waves1 the following analysis connects bed planation to a threshold effect in hindered settling with increasing concentration of noncohesive sediment moving near the bed calculated fluid velocity from the resulting quantitative criterion for this bed transition agrees with extensive laboratory data2 3 in oscillatory flows

hummocky cross stratification is not produced purely under progressive gravity waves hummocky cross stratification is a type of bedding in sedimentary rocks caused by the draping of sand around low steepness three dimensional bedforms this distinctive form of stratification has been thought to be diagnostic of the former action of storm waves and hence its occurrence has been used to reconstruct ancient palaeogeographies and marine processes here i examine theoretical and empirical aspects of hummocky cross stratification pertaining to its origin and argue that the notion that it was produced purely under progressive storm waves is incompatible with observed hummock spacings and possible values of the ratio a under waves a is the amplitude of oscillation near the bed and is the bedform spacing my view is supported by recent observations on naturally occurring hummocky megaripples from the sea floor of the inner atlantic shelf of north america

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

neodymium isotopic composition and concentration in the western north atlantic ocean results from the geotraces ga02 section the neodymium nd isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation the modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete here we present new observational data for nd isotopes and concentrations from twelve seawater depth profiles which follow the flow path of north atlantic deep water nadw from its formation region in the north atlantic to the northern equatorial atlantic samples were collected during two cruises constituting the northern part of the dutch geotraces transect ga02 in 2010 the results show that the different water masses in the subpolar north atlantic ocean which ultimately constitute nadw have the following nd isotope characteristics upper labrador sea water ulsw end 14 2 0 3 labrador sea water lsw end 13 7 0 9 northeast atlantic deep water neadw end 12 5 0 6 northwest atlantic bottom water nwabw end 11 8 1 4 in the subtropics where these source water masses have mixed to form nadw which is exported to the global ocean upper nadw is characterised by end values of 13 2 1 0 2sd and lower nadw exhibits values of end 12 4 0 4 2sd while both signatures overlap within error the signature for lower nadw is significantly more radiogenic than the traditionally used value for nadw end 13 5 due to the dominance of source waters from the nordic seas nwabw and neadw comparison between the concentration profiles and the corresponding nd isotope profiles with other water mass properties such as salinity silicate concentrations neutral densities and chlorofluorocarbon cfc concentration provides novel insights into the geochemical cycle of nd and reveals that different processes are necessary to account for the observed nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column while our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension the results for open ocean seawater demonstrate at an unprecedented level the suitability of nd isotopes to trace modern water masses in the strongly advecting western atlantic ocean

paleocean circulation during the last deglaciation a bipolar seesaw hughen et al 1998 have documented that during the first 200 years of younger dryas time the 14c content of atmospheric co2 increased by 50 and that during the remainder of this 1200 year duration cold event it steadily declined the initial increase in 14c c was likely the result of a reduction in the atlantic s conveyor circulation however were the subsequent radiocarbon decline due to the rejuvenation of this potent heat pump then it is difficult to understand why the climate conditions in the northern atlantic basin remained cold throughout the younger dryas modeling exercises by stocker and wright 1996 mikolajewicz 1998 and schiller et al 1998 show that if the conveyor is terminated the transfer of radiocarbon into the deep sea shifts to the southern ocean thereby stabilizing the atmospheric 14c c ratio paleoclimatic evidence from the antarctic continent suggests that this model based scenario might have been played out in the real world while the younger dryas cooling has been documented in many places around the world including new zealand denton and hendy 1994 sowers and bender 1995 using their 18o in o2 based correlation between the ice core 18o in ice records for antarctica and greenland have demonstrated that in antarctica the younger dryas was a time of maximum warming the point of this paper is that the steep rise in 18o rise in antarctic ice which commenced close to the onset of the younger dryas might have been caused by heat released to the atmosphere in response to an increase in deep sea ventilation in the southern ocean

intensification and variability of ocean thermohaline circulation through the last deglaciation neodymium isotope ratios in the authigenic ferromanganese oxide component in a southeastern atlantic core reveal a history of the global overturning circulation intensity through the last deglaciation from a minimum during the last glacial maximum lgm north atlantic deep water nadw began to strengthen between 18 and 17 kyr cal bp approximately 2000 3000 years before the bolling warming it exhibits a gradually increasing baseline intensity that plateaus in the early holocene tracks increasing northern hemisphere insolation and parallels atmospheric co2 concentration millennial scale fluctuations are superimposed on this baseline nadw increase corresponding to events in northern hemisphere climate records the millennial excursions show sharp increases associated with the pre bolling retreat of continental glaciers and the bolling warming itself a decrease with allerod cooling and a recovery through the younger dryas and early holocene the data confirm a close link between deep ocean circulation and north atlantic climate changes there is no clear linkage with meltwater pulses indicating that rapid meltwater additions did not trigger observable mode changes in nadw production however rapid changes in north atlantic sea ice cover show a strong relationship with the millennial perturbations of nadw flux to the deep southern ocean the data indicate that the baseline intensity of nadw reaching the cape basin is paced by northern hemisphere insolation and that north atlantic sea ice coverage acts as a major amplifying link between the oceans and the atmosphere d 2004 elsevier b v all rights reserved

eruptive history of karymsky volcano kamchatka ussr based on tephra stratigraphy and 14c dating eruptions of the active karymsky stratovolcano began about 5300 6100 14c b p from within a pre existing caldera which formed 7700 14c b p as indicated by 32 14c determinations on buried soils and charcoal the volcano has gone through two major cycles of activity separated by a 2300 year period of repose the first cycle can be divided into two stages 6100 5100 and 4300 2800 b p the earlier stage began with especially intense eruptions of basaltic andesite to dacite the later stage was characterized by moderate strength eruptions of andesite the second cycle which is characterized by weak to moderate intermittent eruptions of andesite started 500 b p and continues to the present eruptive patterns suggest that this cycle may continue for at least another 200 years with an eruptive character similar to that of the recent past

co2 and he degassing at el chichon volcano chiapas mexico gas flux origin and relationship with local and regional tectonics during 2007 2008 three co2 flux surveys were performed on el chichon volcanic lake chiapas mexico with an additional survey in april 2008 covering the entire crater floor including the lake the mean co2 flux calculated by sequential gaussian simulation from the lake was 1 190 march 2007 730 december 2007 and 1 134 g m 2 day 1 april 2008 with total emission rates of 164 9 5 march 2007 59 2 5 december 2007 and 109 6 6 t day 1 april 2008 the mean co2 flux estimated from the entire crater floor area was 1 102 g m 2 day 1 for april 2008 with a total emission rate of 144 5 9 t day 1 significant change in co2 flux was not detected during the period of survey and the mapping of the co2 flux highlighted lineaments reflecting the main local and regional tectonic patterns the 3he 4he ratio as high as 8 1 ra for gases in the el chichon crater is generally higher than those observed at the neighbouring transmexican volcanic belt and the central american volcanic arc the co2 3he ratios for the high 3he 4he gases tend to have the morb like values 1 41 109 and the co2 3he ratios for the lower 3he 4he gases fall within the range for the arc type gases the high 3he 4he ratios the morb like co2 3he ratios for the high 3he 4he gases and high proportion of morb co2 m 25 15 at el chichon indicate a greater depth for the generation of magma when compared to typical arc volcanoes

soil co2 emissions at furnas volcano sao miguel island azores archipelago volcano monitoring perspectives geomorphologic studies and land use planning application accepted for publication in journal of geophysical research copyright 2010 american geophysical union

patagonian origin of glacial dust deposited in east antarctica vostok and dome c during glacial stages 2 4 and 6 abstract the source area of continental dust deposited at both vostok and dome c sites east antarctica during the glacial stages stage 2 18 ka last glacial maximum stage 4 60 ka and stage 6 160 ka of the last two climatic cycles has remained constant the isotopic composition 87 sr 86 sr and 143 nd 144 nd of the ice core dust has been compared with the isotopic composition of the potential source areas antarctica new zealand southern africa australia and south america this comparison reveals the southern south american provenance of the dust for all three glacial periods as has already been shown for the lgm 1 we show that the patagonian loess and the marine shelf sediments from the argentine continental shelf which was variably emerged during glacial periods display different isotopic compositions and that the composition of the patagonian loess best matches the signature of the ice core dust the identification of the patagonian region as the source of the windblown dust deposited over east antarctica during all the latest glacial periods permits a better understanding of paleo atmospheric circulations of the last climatic cycles and a better constraint on the parametrization of dust sources for paleoatmospheric general circulation models

bottoms up sedimentary control of the deep north pacific ocean s end signature the ability to reconstruct past ocean currents is essential for determining ocean circulation9s role in global heat transport and climate change our understanding of the relationship between circulation and climate in the past allows us to predict the impact of future climate driven circulation changes one proposed tracer of past ocean circulation is the neodymium isotope composition e nd of ancient water masses however ambiguities in what governs the e nd distribution in the modern ocean hamper interpretations of this tracer here we present e nd values for marine pore fluids sediments and the overlying water column for three sites in the north pacific we find that ocean bottom water e nd e nd bw in the northeast pacific lies between the value expected for the water mass 3 3 and the measured e nd of sediment pore fluid e nd pw 1 8 moreover e nd pw resembles the e nd of the sediment combined these findings are consistent with recent assessments that sediment pore fluids may be a major source of rare earth elements to the ocean and suggest that the benthic flux of nd from pore fluids exerts the primary control over the deep ocean distribution of e nd

extracting foraminiferal seawater nd isotope signatures from bulk deep sea sediment by chemical leaching the seawater radiogenic neodymium 143nd 144nd isotope signature is an invaluable tool for the reconstruction of past deep water provenance sedimentary foraminifera or fish teeth are among the most reliable archives known for nd isotope based reconstructions of past seawater as the distribution and preservation of these archives are limited the extraction of hydrogenetic ferromanganese oxyhydroxides from bulk sediments provide an easily applicable alternative this method however implies the risk of generating artefacts due to the possible release of non seawater derived nd during the extraction procedure here we revisit and further investigate the reliability of the extraction of seawater derived nd isotope signatures via leaching of bulk deep sea sediments with two commonly used buffered acetic acid and acid reductive mix solutions repeated application of such stepwise leaching procedures to different non decarbonated sediments from distinct settings across the deep atlantic ocean shows pronounced elemental and nd isotope trends during the leaching process in the laboratory our results show that seawater nd isotope compositions are extracted together with carbonates and manganese oxides only at the beginning of the leaching series during chemical extraction the carbonates effectively work as a buffer preventing acid induced mobilisation of fe oxides and volcanogenic material once this buffer is consumed potentially present volcanogenic phases are considerably attacked leading to shifts in the extracted nd isotope signal of up to 12 epsilon units such volcanogenic phases are a significant source of contaminant nd reflected by markedly elevated al nd signatures we consequently propose a revised weak leaching protocol for carbonate bearing deep sea sediments which is simple to use provides excellent agreement with data obtained from uncleaned foraminifera and can be easily screened for contamination

hydrothermal systems of the karymsky volcanic centre kamchatka geochemistry time evolution and solute fluxes abstract karymsky volcanic centre kvc at the middle of the frontal volcanic chain of the kamchatka arc consists of two joined calderas akademii nauk and karymsky volcano and hosts two hydrothermal systems akademii nauk an and karymsky k the an is a typical boiling system with na cl waters tds 1 g l low gas content co2 n2 with deep calculated temperatures of 200 c in contrast springs of the k system have lower temperatures up to 42 c strong gas bubbling tds 2 5 g l and are enriched in hco3 and so42 with mg2 as the main cation there are two intriguing characteristics of the k field i their co2 rich gas 97 mol has the highest 3he 4he ratios ever measured for hydrothermal systems in kamchatka of 8 ra where ra 1 4 10 6 and ii their thermal waters have an unusual cation composition mg na ca after the 1996 sublimnic eruption within an caldera new hot springs appeared close to the eruption site in this paper we synthesize all published and new geochemical data sets the karymsky lake and post 1996 new thermal springs demonstrate exponential decreases in their main dissolved species with a characteristic time of 5 to 8 years the chemistry of an and k springs did not change after the eruption however the concentration of chloride in the lake water approached 35 mg l compared with a background of 8 11 mg l revealing a possible new source of hot water within the karymsky lake all thermal fields of the kvc are drained by the karymsky river with an outflow rate at the source of 2 m3 s flowing out from karymsky lake and at the exit from the karymsky caldera of 4 5 m3 s using the measured solute fluxes at the source an springs and at the exit an k springs the natural heat flux from the two systems can be estimated as 67 mw and 120 mw respectively and 20 t d for the chloride output from both systems

calibration of the carbon isotope composition δ13c of benthic foraminifera the carbon isotope composition 13c of seawater provides valuable insight on ocean circulation air sea exchange the biological pump and the global carbon cycle and is reflected by the 13c of foraminifera tests here more than 1700 13c observations of the benthic foraminifera genus cibicides from late holocene sediments 13ccibnat are compiled and compared with newly updated estimates of the natural preindustrial water column 13c of dissolved inorganic carbon 13cdicnat as part of the international ocean circulation and carbon cycling oc3 project using selection criteria based on the spatial distance between samples we find high correlation between 13ccibnat and 13cdicnat confirming earlier work regression analyses indicate significant carbonate ion 2 6 0 4 10 3 mol kg 1 co32 and pressure 4 9 1 7 10 5 m 1 depth effects which we use to propose a new global calibration for predicting 13cdicnat from 13ccibnat this calibration is shown to remove some systematic regional biases and decrease errors compared with the one to one relationship 13cdicnat 13ccibnat however these effects and the error reductions are relatively small which suggests that most conclusions from previous studies using a one to one relationship remain robust the remaining standard error of the regression is generally 0 25 with larger values found in the southeast atlantic and antarctic 0 4 and for species other than cibicides wuellerstorfi discussion of species effects and possible sources of the remaining errors may aid future attempts to improve the use of the benthic 13c record

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

glacial deep water geometry south atlantic benthic foraminiferal cd ca and δ13c evidence a depth transect of cores from 1268 to 3909 m water depth in the western south atlantic are ideally situated to monitor the interocean exchange of deep water and variations in the relative strength of northern and southern sources of deep water production benthic foraminiferal cd ca and 13c data suggest that glacial north atlantic intermediate water gnaiw extended at least as far south as 28 s in the western south atlantic the core of nutrient depleted water was situated at 1500 m above and below water masses with higher nutrient concentrations when examined in conjunction with published paired cd ca and 13c from intermediate depth cores from other basins it appears that the extent of gnaiw influence on the intermediate waters of the world s oceans was less than suggested previously differentiating among possible pathways for the glacial deep ocean 3 km requires a better understanding of the controls on cd ca and 13c values of benthic foraminifera

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

coherent response of antarctic intermediate water and atlantic meridional overturning circulation during the last deglaciation reconciling contrasting neodymium isotope reconstructions from the tropical atlantic antarctic intermediate water aaiw plays important roles in the global climate system and the global ocean nutrient and carbon cycles however it is unclear how aaiw responds to global climate changes in particular neodymium isotopic composition end reconstructions from different locations from the tropical atlantic have led to a debate on the relationship between northward penetration of aaiw into the tropical atlantic and the atlantic meridional overturning circulation amoc variability during the last deglaciation we resolve this controversy by studying the transient oceanic evolution during the last deglaciation using a neodymium enabled ocean model our results suggest a coherent response of aaiw and amoc when amoc weakens the northward penetration and transport of aaiw decreases while its depth and thickness increase our study highlights that as part of the return flow of the north atlantic deep water nadw the northward penetration of aaiw in the atlantic is determined predominately by amoc intensity moreover the inconsistency among different tropical atlantic end reconstructions is reconciled by considering their corresponding core locations and depths which were influenced by different water masses in the past the very radiogenic water from the bottom of the gulf of mexico and the caribbean sea which was previously overlooked in the interpretations of deglacial end variability can be transported to shallow layers during active amoc and modulates end in the tropical atlantic changes in the aaiw core depth must also be considered thus interpretation of end reconstructions from the tropical atlantic is more complicated than suggested in previous studies

deglacial weakening of the oceanic soft tissue pump global constraints from sedimentary nitrogen isotopes and oxygenation proxies abstract among the many potential explanations for the 80 ppm rise of atmospheric co2 concentrations at the end of the last ice age most involve a weakening of the oceanic soft tissue pump here we use global data compilations of sedimentary nitrogen isotopes and benthic oxygenation proxies to provide a synoptic global perspective on the deglacial soft tissue pump weakening the net change between the last glacial maximum and holocene shows a removal of respired carbon everywhere that proxy data is available with the exception of the upper 1 5 km of the north pacific while excess nitrate accumulated in polar oceans these observations could be explained by intensifying iron limitation a shoaling of organic matter remineralization and or a change in ocean circulation but are inconsistent with a change in the magnitude or position of the southern mid latitude westerlies the net soft tissue pump weakening was front loaded in the early deglaciation 17 5 14 ka when atmospheric 13c and 14c were changing rapidly and appears to have contributed little net change thereafter superimposed on the overall deglacial trend were pronounced transient changes that coincided with variability in the atlantic meridional overturning circulation amoc and bipolar seesaw the seesaw variability is most clearly expressed as anti phased oxygenation changes between the upper 1 5 km of the north pacific and the deep north atlantic consistent with an atlantic pacific ventilation seesaw but it dominated transient variability in records throughout the world although the soft tissue pump seesaw made little contribution to the contrast between the glacial and interglacial states it could have contributed to deglacial variability in atmospheric co2 and might have catalyzed the deglaciation

global co2 emission from volcanic lakes the global co 2 discharge from subaerial volcanism has been estimated at 300 mt yr 1 however estimates of co 2 emissions from volcanic lakes have not been considered in order to improve this information extensive research on co 2 emissions of volcanic lakes worldwide has been performed the observed normalized average co 2 emission rates increase from alkaline 5 5 t km 2 d 1 to neutral 201 2 t km 2 d 1 to acid 614 2 t km 2 d 1 in volcanic lakes taking into account 1 normalized co 2 emission rates 2 the number of volcanic lakes in the world 769 and 3 the fraction and average areas of the investigated alkaline neutral and acid volcanic lakes the estimated global co 2 emission from volcanic lakes is 117 19 mt yr 1 with 94 17 mt yr 1 as deep seated co 2 this study highlights the importance of a revision of the actual global co 2 discharge from subaerial volcanism

southern ocean evidence for reduced export of north atlantic deep water during heinrich event 1 deep sea corals form unique high resolution archives of ocean circulation that can be dated using the decay of uranium to thorium they are abundant in the southern ocean and can provide unprecedented insights into ocean circulation and ocean chemistry on sub millennial time scales in areas where application of traditional paleoceanographic proxies is difficult here we present the first coupled neodymium nd isotope and radiocarbon data from deep sea corals in the drake passage southern ocean adding new constraints on ocean circulation during the last heinrich event h1 16 7 ka the modern day drake passage water column is homogeneous with respect to nd isotopes expressed in epsilon units nd its isotopic value of close to 9 is largely controlled by the mixture of north atlantic deep water and pacific deep water the aragonite of modern drake passage corals reflects this water column value whereas a fossil coral from h1 is significantly higher at 6 4 0 4 we interpret this 2 5 unit shift as a reduction in the influence of north atlantic sourced nd in the southern ocean during h1 this interpretation is supported by a series of radiocarbon analyses on the same sample and is consistent with a twofold or greater reduction in export of north atlantic waters from the atlantic basin combining analyses of radiocarbon and nd isotopes on u series dated deep sea coral skeletons holds great potential for quantification of past ocean ventilation rates

the co2 flux from hydrothermal systems of the karymsky volcanic centre kamchatka abstract the co 2 flux provided by the hydrothermal activity within the karymsky volcanic centre kamchatka was measured and the co 2 balance of the karymsky caldera lake was estimated in the framework of a deep carbon observatory dco project the karymsky volcanic centre located in the se of the kamchatka peninsula in the middle of the modern volcanic front consists of two calderas hosts a caldera lake and is characterized by hydrothermal activity that is manifested at several thermal fields within the akademii nauk an caldera which is filled by a caldera lake the akademii nauk springs discharge boiling water into the lake the lake is drained by the karymsky river that then crosses the caldera of the karymsky volcano karymsky caldera and drains the thermal field of co 2 rich karymsky springs the lake after the 1996 sublimnic eruption is in a steady state condition with the total dynamic co 2 budget of about 4 t day and has a total amount of co 2 stored inside of the lake of around 8000 t the thermal springs of the karymsky caldera drained by the karymsky river enrich the river in dissolved carbon species a total co 2 output of 320 t day from both karymsky centre calderas was estimated carrying around 130 t day carbon species expressed as co 2 as dissolved species hco 3 and co 2 aq and emitting to the atmosphere around 190 t day of co 2 as the diffusion flux from the soil and bubbling emanations from the springs

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

decreased influence of antarctic intermediate water in the tropical atlantic during north atlantic cold events abstract antarctic intermediate water aaiw is a key player in the global ocean circulation contributing to the upper limb of the atlantic meridional overturning circulation amoc and influencing interhemispheric heat exchange and the distribution of salinity nutrients and carbon however the deglacial history of aaiw flow into the north atlantic is controversial here we present a multicore top neodymium isotope calibration which confirms the ability of unclean foraminifera to faithfully record bottom water neodymium isotopic composition e nd values in their authigenic coatings we then present the first foraminifera based reconstruction of e nd from three sediment cores retrieved from within modern aaiw in the western tropical north atlantic our records reveal similar glacial and interglacial contributions of aaiw and a pronounced decrease in the aaiw fraction during north atlantic deglacial cold episodes heinrich stadial 1 hs1 and younger dryas yd our results suggest two separate phases of reduced fraction of aaiw in the tropical atlantic during hs1 with a greater reduction during early hs1 if a reduction in aaiw fraction also reflects reduced amoc strength this finding may explain why in many regions there are two phases of hydrologic change within hs1 and why atmospheric co2 rose more rapidly during early than late hs1 our result suggesting less flow of aaiw into the atlantic during north atlantic cold events contrasts with evidence from the pacific where intermediate depth e nd records may indicate increased flow of aaiw into the pacific during the these same events antiphased e nd behavior between intermediate depths of the north atlantic and pacific implies that the flow of aaiw into atlantic and pacific seesawed during the last deglaciation

how much did glacial north atlantic water shoal observations of 13c and cd ca from benthic foraminifera have been interpreted to reflect a shoaling of northern source waters by about 1000 m during the last glacial maximum with the degree of shoaling being significant enough for the water mass to be renamed glacial north atlantic intermediate water these nutrient tracers however may not solely reflect changes in water mass distributions to quantify the distribution of glacial north atlantic water we perform a glacial water mass decomposition where the sparsity of data geometrical constraints and nonconservative tracer effects are taken into account and the extrapolation for the unknown water mass end members is guided by the modern day circulation under the assumption that the glacial sources of remineralized material are similar to that of the modern day we find a steady solution consistent with 241 13c 87 cd ca and 174 18o observations and their respective uncertainties the water mass decomposition indicates that the core of glacial north atlantic water shoals and southern source water extends in greater quantities into the abyssal north atlantic as previously inferred the depth of the deep northern southern water mass interface and the volume of north atlantic water however are not grossly different from that of the modern day under this scenario the vertical structure of glacial 13c and cd ca is primarily due to the greater accumulation of nutrients in lower north atlantic water which may be a signal of the hoarding of excess carbon from the atmosphere by the glacial atlantic

variability in mid depth ventilation of the western atlantic ocean during the last deglaciation negative stable carbon isotopic excursions have been observed throughout most of the mid depth 1000 3000 m atlantic ocean during heinrich stadial 1 hs1 and the younger dryas yd although there is an agreement that these mid depth excursions were in some way associated with a slowdown of the atlantic meridional overturning circulation amoc there is still no consensus on the precise mechanism s here we present benthic stable carbon and oxygen isotopic 13c and 18o records from five cores from the western equatorial atlantic wea together with published benthic isotopic records from nearby cores we produced a wea depth transect 800 2500 m we compare hs1 and yd data from this transect with data from previously published north and south atlantic cores and demonstrate that the largest negative 13c excursions occurred in the wea during these times moreover our benthic 18o records require the presence of two water masses flowing from the southern ocean bisected by a northern component water ncw given that 18o is a conservative water mass tracer we suggest that 13c was decoupled from water mass composition and does not correspond to simple alternations between northern and southern sourced waters instead 13c behaved non conservatively during hs1 and the yd consistently with our new 231pa 230th record from the wea transect that allowed the reconstruction of amoc strength we hypothesize that the negative 13c excursions reflect an increase in the residence time of ncw in response to a weakened amoc allowing for a marked accumulation of 13c depleted respired carbon at the mid depth wea

rare earth element transport in the western north atlantic inferred from nd isotopic observations the isotopic composition of nd in the water column from several western north atlantic sites and formational areas for north atlantic deep water shows extensive vertical structure at all locations in regions where a thermocline is well developed large isotopic shifts 2 to 3 units are observed across the base of the thermocline regions without a thermocline are characterized by much more gradual shifts in isotopic composition with depth in general the data reveal an excellent correlation between the nd isotopic distribution in the western north atlantic water column and the distribution of water masses identified from temperature and salinity characteristics nadw as identified from t s properties is also characterized by a well defined isotopic composition having nd 0 13 5 0 5 this signature is associated with waters identified as nadw from high latitudes near formational areas in the labrador sea down to the equatorial region the isotopic signature of nadw would appear to be formed by a blend of more negative waters originating in the labrador sea nd 0 18 and more positive waters originating in the overflows from the norwegian and greenland seas nd 0 8 to 10 and is consistent with classical theories on the formation of nadw the isotopic signature of nadw is propagated southward to the equator where it is gradually being thinned out by mixing from above and below with more radiogenic nd associated with northward spreading antarctic intermediate and bottom waters the preservation of the isotopic signature of nadw over these large distances indicate that the ree undergo extensive lateral transport the isotopic composition of nd is largely conservative over the time scales of mixing within the atlantic in spite of the intrinsic nonconservative behavior of neodymium nd concentration gradients generally show surface waters to be depleted in nd relative to deep waters which must require vertical transport processes however isotopic differences in the water column preclude the local downward transport of ree from the surface into underlying deep waters as a simple explanation of the concentration gradient the apparent decoupling of ree in nadw from overlying local surface waters and the increasing concentration with depth provide a conflict with simple vertical transport mechanisms that is not yet resolved

separating biogeochemical cycling of neodymium from water mass mixing in the eastern north atlantic abstract the radiogenic neodymium nd isotope ratio 143nd 144nd expressed in e nd is being used as a tracer in paleo and modern ocean circulation however the mechanisms controlling input distribution and internal cycling are far from understood for example globally nd concentration nd commonly follows patterns of nutrient tracers generally increasing with depth below the thermocline while e nd tends to reflect the water masses which has often been referred to as the nd paradox here we present dissolved nd isotopes and concentrations at unprecedented vertical and spatial resolution from the eastern part of the us geotraces north atlantic zonal transect gulf of cadiz mauritanian shelf cape verde islands the nd of all samples ranges from 12 3 to 36 7 pmol kg with lowest nd usually found within the layer of highest chlorophyll a levels chl max suggesting removal through scavenging the nd isotope compositions range between e nd 13 4 and 9 9 with lower values at the surface within the extension of the saharan dust plume and a benthic nepheloid layer bnl less negative values are found in oligotrophic surface waters mediterranean outflow water mow and near the cape verde islands overall water mass mixing derived from e nd is best visible at the strait of gibraltar where mow enters the atlantic ocean most of the sub thermocline e nd varies within a small range with poor water mass distinction due to the dominance of north atlantic deep water high surface nd associated with more negative e nd is interpreted to be the result of dust deposition and dissolution local nd maxima with no apparent change in e nd compared to ambient seawater observed within a zone of minimum oxygen concentration omz at 500 m depth off mauritania suggest minor input of lithogenic nd but a rather high contribution through desorption of previously scavenged nd that is saharan dust in this area has only a minor influence on the isotope composition of water below the uppermost surface layer the low e nd values and elevated nd within the bnl on the other hand indicate release from detrital material our new high resolution dataset gives valuable insights into the nd distribution near continental margins influenced by high atmospheric inputs and changing oxygen conditions we show how vertical and lateral processes overlap to produce the observed nd distribution bringing us forward in understanding the nd paradox

antarctic intermediate water circulation in the south atlantic over the past 25 000 years antarctic intermediate water is an essential limb of the atlantic meridional overturning circulation that redistributes heat and nutrients within the atlantic ocean existing reconstructions have yielded conflicting results on the history of antarctic intermediate water penetration into the atlantic across the most recent glacial termination in this study we present leachate foraminiferal and detrital neodymium isotope data from three intermediate depth cores collected from the southern brazil margin in the south atlantic covering the past 25 kyr these results reveal that strong chemical leaching following decarbonation does not extract past seawater neodymium composition in this location the new foraminiferal records reveal no changes in seawater nd isotopes during abrupt northern hemisphere cold events at these sites we therefore conclude that there is no evidence for greater incursion of antarctic intermediate water into the south atlantic during either the younger dryas or heinrich stadial 1 we do however observe more radiogenic nd isotope values in the intermediate depth south atlantic during the mid holocene this radiogenic excursion coincides with evidence for a southward shift in the southern hemisphere westerlies that may have resulted in a greater entrainment of radiogenic pacific sourced water during intermediate water production in the atlantic sector of the southern ocean our intermediate depth records show similar values to a deglacial foraminiferal nd isotope record from the deep south atlantic during the younger dryas but are clearly distinct during the last glacial maximum and heinrich stadial 1 demonstrating that the south atlantic remained chemically stratified during heinrich stadial 1