middle devonian olistostromes in the rheno hercynian zone rheinisches schiefergebirge an indication of back arc rifting on the southern shelf of laurussia abstract the rheinisches schiefergebirge in the rheno hercynian zone of the mid european variscides was geographically situated on laurussia s southern shelf during the devonian in its eastern part lahn dill area givetian coarse clastic sediments formerly misinterpreted as transgressional conglomerates are recognised as olistostrome deposits intercalated in basinal sediments that document a phase of rifting on the southern shelf of laurussia the clastic components redeposited as olistolithes and rounded boulders are locally derived rocks of emsian and givetian age the olistostromes show facies patterns comparable with other syn rift deposits the proximal facies is characterised by olistolithes and slideflow debrites overlain by debrites and intercalated with turbidites the distal facies is represented by intercalation of debrites and turbidites both grade upwards into basinal sedimentation based on conodont stratigraphy the redeposition lasted from the middle varcus zone to the disparilis zone during the middle varcus zone footwall uplift raised the sedimentary column of the source area by about 500 m above which brought it above sea level rifting of the laurussian shelf as a result of hinterland transtension and extension caused by the oblique collision of peri gondwana with laurussia provides the most plausible explanation for the development of the olistostromes olistolithes and slideflow debrites in the eastern rheinisches schiefergebirge

fertilizing potential of volcanic ash in ocean surface water the fertilization potential of newly erupted and well preserved ash from the 2000 hekla eruption in iceland was measured for the first time by flow through experiments as previously shown 1 the north atlantic ocean including the subarctic seas surrounding iceland is the largest net sink of the world s oceans for atmospheric co 2 owing to biological drawdown during summer 2 almost complete consumption of phosphate in chlorophyll rich areas of the north atlantic ocean might limit primary production and 3 in the southern pacific ocean and parts of the equatorial pacific ocean iron might limit primary production we found through laboratory experiments that volcanic ash exposed to seawater initially releases large amounts of adsorbed phosphate 1 7 mmol g 21 h 21 iron 37 0 mmol g 21 h 21 silica 49 5 mmol g 21 h 21 and manganese 1 7 mmol g 21 h 21 dissolution of acid aerosols adsorbed to the surface of the ash caused the high initial release of major and trace elements because of the instantaneous dissolution of adsorbed components when newly erupted volcanic ash comes in contact with the ocean surface water macronutrients and bioactive trace metals are released fast enough to become available to support primary production

rapid releases of metal salts and nutrients following the deposition of volcanic ash into aqueous environments deposition of volcanic ash into aqueous environments leads to dissolution of adsorbed metal salts and aerosols increasing the bioavailability of key nutrients volcanogenic fertilization events could increase marine primary productivity leading to a drawdown of atmospheric co2 here we conduct flow through experiments on unhydrated volcanic ash samples from a variety of locations and sources measuring the concentrations and fluxes of elements into de ionized water and two contrasting ocean surface waters comparisons of element fluxes show that dissolution of adsorbed surface salts and aerosols dominates over glass dissolution even in sustained low ph conditions these surface ash leachates appear unstable decaying in situ even if kept unhydrated volcanic ash from recent eruptions is shown to have a large fertilization potential in both fresh and saline water fluorine concentrations are integral to bulk dissolution rates and samples with high f concentrations display elevated fluxes of some nutrients particularly fe si and p bio limiting micronutrients are released in large quantities suggesting that subsequent biological growth will be limited by macronutrient availability importantly acidification of surface waters and high fluxes of toxic elements highlights the potential of volcanic ash leachates to poison aqueous environments in particular large ph changes can cause undersaturation of caco3 polymorphs damaging populations of calcifying organisms deposition of volcanic ash can both fertilize and or poison aqueous environments causing significant changes to surface water chemistry and biogeochemical cycles

middle late pleistocene deep water circulation in the southwest subtropical pacific 1 the modern 13cdic distribution in southwest subtropical pacific deep waters is consistent with a regional mixing regime between water masses of open pacific ocean and tasman sea origin this mixing regime is reconstructed across the middle late pleistocene using a record of benthic foraminiferal 13c in a sediment core from the new caledonia trough the relative influence on the mixing regime from open pacific ocean deep waters is seen to be significantly reduced during glacial in comparison to interglacial stages over the past 1 1 ma the spatial 13c gradient in the southern ocean between deep waters entering the tasman sea and the open pacific ocean is shown to be consequently greater during glacial than interglacial stages but was generally reduced across the period of the middle pleistocene transition the existence of strong spatial chemical gradients in the glacial southern ocean limits its capacity to act as an enhanced sink for atmospheric carbon

experimental tests for particle size dependent bioturbation in the deep ocean the potential for particle size dependent bioturbation rates was experimentally tested at 1 240 m in the santa catalina basin eastern pacific spherical glass bead tracers in five size classes 816 17 31 32 62 63 125 and 126 420 m were spread over the sediment surface and tube cored 997 d later downcore concentrations of glass beads were enumerated in each of the five size categories and page s l test was used to test the null hypothesis of equal vertical penetration of all size classes of tracer in all cores the null hypothesis was rejected finer tracers penetrated deeper into the sediment in two of the three cores vertical biodiffusivities were computed from concentration profiles of downcore tracers these also showed size dependence with biodiffusivities ranging from 1 cm2 yr for the 8 1 6 pm fraction to 0 1 cm2 yr for the 1 25 420 pm size class these data demonstrate that vertical bioturbation rates are particle size dependent in santa catalina basin the likely cause is preferential ingestion and downward transport of fine particles by deposit feeders

glacial interglacial ocean climate variability from planktonic foraminifera during the mid pleistocene transition in the temperate southwest pacific odp site 1123 abstract planktonic foraminiferal assemblages and artificial neural network estimates of sea surface temperature sst at odp site 1123 41 47 2 s 171 29 9 w 3290 m deep east of new zealand reveal a high resolution history of glacial interglacial g i variability at the subtropical front stf for the last 1 2 million years including the mid pleistocene climate transition mpt most g i cycles of 100 kyr duration have short periods of cold glacial and warm deglacial climate centred on glacial terminations followed by long temperate interglacial periods during glacial deglacial transitions maximum abundances of subantarctic and subtropical taxa coincide with sst minima and maxima and lead ice volume by up to 8 kyrs such relationships reflect the competing influence of subantarctic and subtropical surface inflows during glacial and deglacial periods respectively suggesting alternate polar and tropical forcing of southern mid latitude ocean climate the lead of ssts and subtropical inflow over ice volume points to tropical forcing of southern mid latitude ocean climate during deglacial warming this contrasts with the established hypothesis that southern hemisphere ocean climate is driven by the influence of continental glaciations based on wholesale changes in subantarctic and subtropical faunas the last 1 2 million years are subdivided into 4 distinct periods of ocean climate 1 the pre mpt 1185 870 ka has high amplitude 41 kyr fluctuations in sst superimposed on a general cooling trend and heightened productivity reflecting long term strengthening of subantarctic inflow under an invigorated antarctic circumpolar current 2 the early mpt 870 620 ka is marked by abrupt warming during mis 21 followed by a period of unstable periodicities within the 40 100 kyr orbital bands decreasing sst amplitudes and long intervals of temperate interglacial climate punctuated by short glacial and deglacial phases reflecting lower meridional temperature gradients 3 the late mpt 620 435 ka encompasses an abrupt decrease in the subantarctic inflow during mis 15 followed by a period of warm equable climate poorly defined low amplitude g i variations in ssts during this interval are consistent with a relatively stable stf and evenly balanced subantarctic and subtropical inflows possibly in response to smaller less dynamic polar icesheets 4 the post mpt 435 0 ka is marked by a major climatic deterioration during mis 12 and a return to higher amplitude 100 kyr frequency sst variations superimposed on a long term trend towards cooler ssts and increased mixed layer productivity as the subantarctic inflow strengthened and polar icesheets expanded

simulated influence of carbon dioxide orbital forcing and ice sheets on the climate of the last glacial maximum a coupled atmosphere ocean sea ice model is used to investigate the climate of the last glacial maximum 21 000 years ago and the relative climate forcing effects of atmosphere co2 the earth s orbital parameters and ice sheet albedo tropical temperatures are found to be 2 2 c less than today s slightly colder than indicated by the climap palaeoclimate reconstruction this result is consistent with a low to medium climate sensitivity to radiative perturbations temperatures are colder still in the northern north atlantic region owing to a weakening and shallowing of the thermohaline circulation a sensitivity analysis suggests that changes in ocean circulation since the last glacial maximum have not contributed directly to the global mean temperature change since that time

rhenium and molybdenum enrichments in sediments as indicators of oxic suboxic and sulfidic conditions of deposition abstract the trace elements re and mo both behave conservatively in seawater yet are strongly enriched in reducing sediments their potential for authigenic enrichment above crustal concentrations is greater than for many other elements due to the high ratio of metal sw metal crust we present sedimentary re and mo data from box and multi cores spanning a range of redox conditions from well oxygenated sites to locations with substantial sulfide concentrations at the oxic sites re and mo as expected accumulate at concentrations close to their crustal abundances re shows substantial enrichment in suboxic absence of o 2 and h 2 s sediments of the sea of japan in sediments within the oxygen minimum of the pakistan margin as well as in sediments underlying the sulfide bearing waters of the black sea and saanich inlet re enrichment occurs in these cores just below the depths of fe and u reduction only in the sediments underlying the sulfidic waters of the black sea and saanich inlet is there substantial authigenic mo accumulation absence of re and mo enrichments in sediment trap samples from the sulfide bearing basins suggests that the addition of both metals occurs at or below the sediment water interface the re and mo concentration profiles are modeled to hindcast the removal depth of re and mo in the sediments which along with the re mo ratio determine whether oxic suboxic or sulfidic conditions were present in the water column or in the sediments in the past using this approach historical redox conditions can be inferred even in environments such as continental margins where a substantial lithogenic component can obscure authigenic enrichments of other metals

coccolithophore carbonate during the last 450 ka in the nw pacific ocean odp site 1209b shatsky rise this study focuses on pleistocene holocene sediments from the shatsky rise ocean drilling program site 1209b nw pacific ocean we quantify the contribution of calcite made by coccoliths in oceanic sediments investigating the role of calcareous nannoplankton during the last 450 ka coccolith carbonate constitutes 60 90 of bulk carbonate coccolith carbonate accumulation rates cars and caco3 fine fraction confirm that coccolithophores are major contributors to the carbonate export and accumulation primary productivity shows highest values from marine isotope stage mis 12 to 8 thereafter although coccolith calcite content remains high other sediment components such as as foraminifera and biogenic opal seem to be favored perhaps related to an increase in fertilization by eolian dust our results demonstrate the important role of coccolithophore production and sedimentation on the regulation of ocean carbonate chemistry on time scales 1000 100 000 years on glacial interglacial scales coccolithophore productivity could have affected deep water saturation by buffering deep sea co2 through increased carbonate dissolution episodes spectral and wavelet analyses are consistent with cars primarily driven by glacial interglacial variability and obliquity controlled changes coccolith based paleoceanographic reconstructions allow us to establish that during the last 450 ka the mid latitudes of the nw pacific are controlled by the dynamics of the el nino southern oscillation perturbations and boreal monsoon system

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

the maesan fan delta miocene pohang basin se korea architecture and depositional processes of a high gradient fan delta fed slope system the maesan fan delta fed slope system in the miocene pohang basin occurs between two gilbert type fan deltas detailed analysis of sedimentary facies and bed geometry reveals that the sequence is represented by 13 sedimentary facies these facies can be organized into three facies associations representing distinct depositional environments alluvial fan facies association i steep faced slope facies association ii and basin plain facies association iii subaerial debris flows and dense inertia dominated currents were transformed into subaqueous sediment gravity flows in steep faced slope environments further downslope these flows were channelized and formed lobate conglomerate and sandstone bodies at the terminal edge of the channels or chutes interchannel and interlobe areas were dominated by homogeneous mudstone and muddy sandstone deposited by suspension settling of fine grained materials part of the steep faced slope deposits experienced large scale slides and slumps the chutes channels lobes and splays on the steep faced slope of the maesan system are similar to those in modern subaqueous coarse grained fan delta systems

mean mixed depth of sediments the wherefore and the why the activities and consequently the bioturbational effects of deposit feeding organisms are largely restricted to a narrow surficial zone of marine sediments with a worldwide environmentally invariant mean of 9 8 cm with a standard deviation of 4 5 cm currently available theories of infaunal behavior cannot predict quantitatively this observation a new simple model that accounts for the feedback between resource food abundance its reactivity and the intensity of bioturbation leads to a quantitative estimate of 9 7 cm this model constitutes a fundamental advance in our understanding bioturbation

carbonate dissolution fluctuations in the western equatorial pacific during the late quaternary planktonic foraminiferal test fragmentation in three cores along a depth transect from the western equatorial pacific erdc 93p 1619 m rc17 177 2600 m v28 238 3120 m thompson 1976 were examined for the last 500 kyr at sample intervals from 2 5 to 5 kyr to study the fluctuations of dissolution in the western equatorial pacific the age models were constructed by correlating the 18o records with the specmap stack imbrie et al 1984 results showed that intermediate and deep waters experienced the same patterns of dissolution through climatic cycles fragmentation varied with a greater amplitude and the carbonate ion concentration changed less in the deep than in the intermediate water dissolution has significant variance distributions and coherencies with 18o over the 100 41 and 23 kyr periods of orbital variations dissolution maxima lag ice volume minima by 6 to 20 kyr the dissolution variability was consistent with recent geochemical models which seek to explain the reduction of atmospheric co2 concentration at the last glacial maximum broecker 1982 boyle 1988

authigenic uranium in atlantic sediments of the last glacial stage a diagenetic phenomenon cores from three different atlantic localities equatorial cape verde rise and porcupine abyssal plain are shown to have anomalous high u contents 5 8 ppm total in sediments laid down during the last glacial stage 12 24 ky bp radiocarbon data demonstrate that the sediments hosting the peak u levels were accumulated at rates similar to those immediately above and below all the cores exhibit maximum mn levels characteristic colour changes and maximum u levels in the same sequence with increasing depth in core on the evidence of the similarities between the cores and pore water u data from a porcupine abyssal plain site it is proposed that the authigenic u enrichments are syndiagenetic and possibly active no correlation is observed between sediment authigenic u and corg contents the source of enrichment is bottom water u which has diffused downwards into the sediments to be sorbed at a particular redox level located 10 30 cm below the oxic post oxic boundary marked by the colour change the magnitude of the enrichments is caused by the persistence of this boundary at a particular level as a result of the decrease in mean sediment accumulation rate between the last glacial stage 5 2 up to at least 19 1 cm ky 1 and the holocene 2 2 4 1 cm ky 1 similar accumulation rate contrasts are expected to be widespread in the atlantic and the implications for previous reported work particularly from the mid atlantic ridge are discussed

climatic change and caco3 preservation an 800 000 year bathymetric reconstruction from the central equatorial pacific ocean sixteen deep sea cores from the central equatorial pacific are used to reconstruct a continuous 800 000 year 800 kyr record of bathymetric variations in carbonate preservation as measured by calcium carbonate caco3 content the depth of the sedimentary lysocline has fluctuated markedly in conjunction with late pleistocene climate cycles while the carbonate critical depth ccrd which is the water depth where the sediments contain 10 caco3 has remained relatively constant as a result the depth of the lysocline controls the bathymetric position and thickness of the caco3 transition zone defined as the depth from the lysocline to the ccrd modern and interglacial aged sediments show poor caco3 preservation and thick caco3 transition zones glacial aged sediments show good preservation and deep thin zones due to the deepening of the lysocline detailed comparison of the caco3 preservation and oxygen isotope records from the central equatorial pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages during the nine major glacial stages of the last 800 kyr the lysocline deepened by at least 400 to 800 m this deepening indicates an increase in the abyssal carbonate ion concentration co3 and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate saturated water mass the bottom of the transition zone has remained at a relatively constant depth during the brunhes chron indicating a balance between caco3 sedimentation and dissolution in the deepest waters of the central equatorial pacific

progress toward a multi basin calibration for quantifying deep sea calcite preservation in the tropical subtropical world ocean article i nfo the development of a quantitative and multi basin deep sea calcite preservation proxy is important for a better understanding of the marine carbonate system both in modern sediments and in down core work we present caco3 preservation data from 89 core top samples in tropical and subtropical areas of the pacific atlantic and indian oceans we observe that the globorotalia menardii fragmentation index mfi has potential to trace deep sea caco3 dissolution quantitatively across the tropical subtropical world ocean this is evident in the robust relationship between mfi and bottom water calcite under saturation in six depth transects with markedly different bottom water co3 2 saturation states we also found a strong relationship between mfi and modeled estimates of percent caco3 dissolved at our core top locations corroboration for mfi s dissolution trend in the subtropics comes from the concurrent drop in size normalized shell weight of globorotalia truncatulinoides specimens with increasing co3 2

intensified deep pacific inflow and ventilation in pleistocene glacial times the production of cold deep waters in the southern ocean is an important factor in the earth s heat budget1 the supply of deep water to the pacific ocean is presently dominated by a single source the deep western boundary current east of new zealand here we use sediment records deposited under the influence of this deep western boundary current to reconstruct deep water properties and speed changes during the pleistocene epoch in physical and isotope proxies we find evidence for intensified deep pacific ocean inflow and ventilation during the glacial periods of the past 1 2 million years the changes in throughflow may be directly related to an increased production of antarctic bottom water during glacial times possible causes for such an increased bottom water production include increasing wind strengths in the southern ocean or an increase in annual sea ice formation leaving dense water after brine rejection and thereby enhancing deep convection we infer also that the global thermohaline circulation was perturbed significantly during the mid pleistocene climate transition between 0 86 and 0 45 million years ago

an exceptionally widespread ignimbrite with implications for pyroclastic flow emplacement pumice rich pyroclastic flows leave deposits called ignimbrites1 which are common in the eruption records of arc and intracontinental volcanoes2 3 pyroclastic flows represent the most dangerous manifestation of volcanism4 because of their volumes rapid emplacement at high temperatures and capacity to extend 100 km from the source however maximum distances travelled and extents of areas destroyed by pyroclastic flows remain poorly known historic examples have been relatively small the largest reaching to only 35 km from the vent5 but prehistoric ignimbrites over 150 km across are known3 6 10 the largest ignimbrites are invariably partly buried or eroded and only minimum estimates of their size and hence of their destructive capacity can be made here we describe the l myr old kidnappers ignimbrite erupted from the taupo volcanic zone in new zealand which we have correlated for 385 km and which thus represents the most wide spread ignimbrite yet known we suggest that this wide distribution primarily reflects a coupling of high initial flow velocities with large mass fluxes and that favourable flow paths and emplacement of flows over a wet substrate may have aided their mobility

can the morphology of deep sea benthic foraminifera reveal what caused their extinction during the mid pleistocene climate transition abstract over 100 cosmopolitan species of deep sea benthic foraminifera extinction group ext gp became extinct during the late pliocene middle pleistocene 3 6 0 55 ma most had elongate cylindrical tests and terminal apertures with complex modifications this study provides new hypotheses on the functions of the morphologies that characterised the ext gp and how these features could have been associated with their demise from our functional morphological analysis we infer that i their elongate cylindrical or flabelliform tests combined with fine perforations and a complex terminal apertural face are indicative of infaunal k strategists with a low rate of metabolism and ii their complex apertural faces may also have been an adaptation for gathering or processing their specific phytodetrital food we propose three alternative hypotheses for the cause of these extinctions and where possible test them using our high resolution micropaleontological and geochemical record through the last 1 07 ma in lower bathyal site md 97 2114 in the sw pacific ocean hypothesis 1 is that the ext gp species were unable to adapt to increased variability in the overall quantity or pulsed seasonality of the food supply to the sea floor and were out competed by opportunistic r strategist benthic foraminifera this is supported by the highly variable and increasing abundance of opportunistic foraminifera at our study site during the final phase of the extinction in the mid pleistocene climate transition mpt we doubt however that there was increased variability in phytoplankton productivity throughout the world s oceans sufficient to bring about the global demise of the ext gp hypothesis 2 is that lowered pco2 during increasingly severe mpt glacials which coincided with the final phases of the extinction may have caused the decline and possible loss of the ext gp s phytoplankton food source declining pco2 during neogene cooling was coeval with declining relative abundance of the ext gp and reticulofenestrid nannofossils but the final demise of this latter phytoplankton group occurred slightly later than the mpt in our study site and cannot be implicated with the extinction if this hypothesis has any validity maybe the phytoplankton group left no fossil record our third alternative hypothesis is that maybe our ext gp had much common dna which made them the selective target of pathogens that caused their extinction this does not easily explain their earlier disappearance at abyssal depths than at bathyal depths in our study region which can be accommodated by hypotheses 1 and 2

magnetic proxy for the deep pacific western boundary current variability across the mid pleistocene climate transition the deep western boundary current dwbc inflow to the sw pacific is one of the largest transporting 40 of the total input of deep water to the world s oceans here we use a sedimentary record from the giant piston core md97 2114 collected on the northern flank of the chatham rise located at 1935 m water depth east of new zealand to investigate dwbc variability during the pleistocene epoch when the period of glacial cycles changed progressively from a 41 kyr to 100 kyr rhythm magnetic grain size may be directly related to orbitally forced fluctuations in the strength of the upper circumpolar deep water ucdw through its interaction with terrigenous sediments supplied from the south and west the long term trends in magnetic properties are characterized by two main perturbations centered at 870 ka marine isotope stage mis 22 450 ka mis 12 which is broadly consistent with the inferred perturbation during the mid pleistocene climate transition based on sedimentological paleocurrent reconstruction from ocean drilling program site 1123 located at 3290 m water depth in the main core of the dwbc flow on the north chatham drift this similarity suggests that both the upper and middle cdw are modulated by similar processes and fluctuations of antarctic bottom water production could be directly responsible for this deep pacific ocean inflow variability over the past 1 2 ma

redox zonation of elements at an oxic post oxic boundary in deep sea sediments abstract deep sea sediments generally provide limited evidence of redox control on the post depositional redistributions of elements this is because only a fraction of any element is reactive and observed elemental distributions are the result of a number of competing processes which are simultaneously active so that redox effects are not dominant a detailed investigation is reported of a core which is unusual in showing unequivocal evidence of direct redox control operating in a homogeneous environment that is relatively free from competing processes a progressive oxidation front has migrated slowly downwards into a uniform turbidite over a long period ca 250 ky the reactive fractions of several redox sensitive elements now show a remarkable degree of organisation around the redox boundary of this front with the different elements exhibiting individual responses solid phase enrichments are not coincident but are arranged in a clear succession of concentration peaks along the redox gradient from oxic to postoxic conditions the succession is mn i fe se and pt cu and pb v zn and sb and u the movement directions of most elements can be inferred from the peak shapes against the homogeneous turbidite background composition the system seems to have been essentially isolated within the sediment for most elements so that no loss or gain can be ascribed to redox processes exceptions are u and v which have been augmented by uptake from ocean bottom waters into the sediments by an efficient redox trap mechanism

reconstruction of the last deglaciation deconvolved records of δ18o profiles micropaleontological variations and accelerator mass spectrometric14c dating bioturbation acts as a low pass filter in displacing and reducing the amplitudes of stratigraphic signals this often leads to a loss of high frequency events in the stratigraphic record in addition when considering an isotopic signal 18o 14c measured in stratigraphic carriers such as foraminifera bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record

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

quaternary carbonate record from the equatorial indian ocean and its relationship with productivity changes abstract the caco3 content in quaternary deep sea sediments from pacific and atlantic oceans have been suggested to respond differently to glacial interglacial cycles caco3 contents are highest during glacials in the pacific but highest during interglacials in the atlantic ocean it is not yet clear as to whether a pacific or an atlantic pattern of caco3 fluctuations dominates the indian ocean we have analyzed the ocean drilling program odp site 709a from the western equatorial indian ocean for the last 1370 ka to determine the relationships between percentages and fluxes of caco3 and quaternary paleoclimatic changes we also analyzed the coarse 25 m and fine 18 o of the planktonic foraminifera globigerinoides ruber this indicates that caco3 fluctuations at this site do not show either a pacific or an atlantic pattern of caco3 fluctuations fluxes of caco3 0 38 to 2 46 g cm 2 ka 1 in total sediment and ba al ratios 0 58 to 3 93 g cm 2 ka 1 show six fold variability through the last 1370 ka which points out that productivity changes are significant at this site fluxes of the fine caco3 component demonstrate a 26 fold change 0 02 to 0 52 g cm 2 ka 1 whereas the coarse caco3 component exhibit eight fold change 0 13 to 1 07 g cm 2 ka 1 this suggests that productivity variations of calcareous nannofossils are greater in comparison with the foraminifera on the other hand mean values of coarse caco3 fluxes are higher compared to those of fine caco3 which reveals that the foraminifera contribute more to the bulk caco3 flux than the calcareous nannofossils in the equatorial indian ocean

bioturbation short lived radioisotopes and the tracer dependence of biodiffusion coefficients bioturbation refers to the mixing of sediment particles resulting from benthic faunal activity it is the dominant particle mixing process in most marine sediments and exerts an important control on diagenetic processes in models bioturbation is usually treated as a diffusive process where the biodiffusion coefficient db characterizes the biological mixing intensity biodiffusion coefficients are classically computed by fitting a diffusive model to vertical profiles of particle bound radioisotopes one peculiar observation is tracer dependence db values from short lived tracers tend to be larger than those obtained from long lived tracers from the same site recent theoretical work based on random walk theory and lattice automaton bioturbation simulations labs has suggested that this tracer dependence is simply a model artifact and has concluded that the biodiffusion model is not applicable to the short observational time scales associated with short lived radioisotopes here we have compiled a global dataset of db values obtained from different radiotracers to assess tracer dependence from a data perspective tracer dependence is significant in low mixing environments like slope and deep sea sediments but is not present in intensely mixed coastal areas tracer dependence is absent when the number of mixing events is larger than 20 or the potential length scale is greater than 0 5 cm roughly this comes down to tracer derived db values greater than 2 cm2 yr 1 this condition is met for 68 50 and 8 of published db values obtained from coastal continental slope and abyssal environments respectively these results show that short lived radioisotopes are suitable to quantify biodiffusion mixing in sedimentary environments featuring intense bioturbation

the diffusive tortuosity of fine grained unlithified sediments abstract use of fick s first law to estimate solute fluxes is arguably the most common and important calculation related to the geochemistry and environmental chemistry of fine grained unlithified sediments in such porous media the diffusion coefficient in this law must be reduced by the square of the tortuosity to account for the longer diffusive paths experimental methods to estimate tortuosity are specialized or time consuming and not routinely done an analysis of available data shows that tortuosity is accurately correlated to readily measured porosity values through the simple relation 2 1 l n 2

late pleistocene evolution of the ocean s carbonate system abstract we demonstrate that the carbonate record from a single site ocean drilling program site 1089 in the deep south atlantic represents a qualitative high resolution record of the temporal evolution of the carbonate saturation state of the deep sea the record is especially notable because it is free from many of the complications that limit other records low sedimentation rates blurring by chemical erosion bioturbation etc the pattern of carbonate variability is characteristic of indo pacific cores with high carbonate glacials and low carbonate interglacials wt carbonate lags changes in benthic 18 o by an average of 7 6 kyr and carbonate variations are in phase with the rate of change first derivative of benthic 18 o intense dissolution occurs at the transition from interglacial to glacial periods and increased preservation occurs during deglaciations these observations represent two fundamentally different responses of the marine carbonate system the lagged response of carbonate to 18 o reflects a steady state mass balance process whereby the lysocline adjusts to maintain alkalinity balance between riverine input and marine burial the site 1089 carbonate signal is remarkably similar to inferred changes in the sr ca of seawater for the past 250 kyr which implies that both carbonate dissolution and seawater sr ca may be controlled by sea level induced changes in the location of carbonate deposition shelf basin fractionation during glacial to interglacial cycles the transient change in preservation during the transitions into and out of glacial stages reflects a response of the carbonate system to a redistribution of alkalinity and dic in the ocean i e carbonate compensation comparison of the site 1089 carbonate and vostok p co 2 records suggests a role of deep sea co 3 2 variations for governing at least some second order features of the atmospheric p co 2 signal in order to quantify this role however measurement of indices of dissolution along a true depth transect will be required to estimate the magnitudes of changes in deep sea co 3 2

organic carbon flux and organic carbon to calcite flux ratio recorded in deep sea carbonates demonstration and a new proxy 1 theoretical considerations indicate that degree of bottom water calcite saturation organic carbon flux and the ratio of that flux to the calcite flux all are reflected in the carbonate preservation record of deep sea sediments separating the influence of these various factors on the record depends first on estimating the percent of the calcite flux which is dissolved at the seabed we have developed a new proxy for percent dissolved calcite by calibrating a foraminiferal fragmentation index to biogeochemical model derived data application of our proxy combined with geochemical modeling to the surface sediments of the eastern equatorial pacific eep demonstrates the need for all three of the variables listed above to account for the observations further we used reverse modeling to map the ratio of the biotic fluxes across the eep we observe a coherent regional pattern with highest ratio values as expected associated with areas of upwelling particularly along south america our proxy appears to be unaffected by carbonate sediment properties such as percent calcite in samples or the amount of coarse fraction 63 m in the calcareous portion of the sediments therefore it reflects primarily the geochemical environment rather than characteristics of seabed deposits

caco3 dissolution in california continental margin sediments the influence of organic matter remineralization in situ benthic flux chamber and oxygen microelectrode and shipboard porewater results have been used to quantify sea floor dissolution of caco3 on the continental rise adjacent to central california usa the porewater distributions and benthic fluxes of o2 no3 ta ca2 13c and tic are interpreted using a numerical simulation of organic matter remineralization and caco3 dissolution in marine sediments the processes considered in the simulation include organic matter oxidation by o2 no3 and so42 caco3 dissolution and precipitation hs and nh4 oxidation and sediment mixing and sediment accumulation calculated benthic fluxes of o2 no3 ta tic 13c and ca2 porewater concentrations of o2 no3 and nh4 and sediment distributions of organic carbon caco3 excess 210pb and 14c agree well with the measurements benthic fluxes of alkalinity and inferred caco3 dissolution rates cannot be explained on the basis of dissolution driven solely by bottom water undersaturation if the influence of metabolically produced co2 is included benthic fluxes are fully reconciled however this is in agreement with benthic chamber ca2 and 13c results that independently imply substantial caco3 dissolution in these sediments the above observations are in contrast to those reported by jahnke et al 1994 for the west african continental rise and the western equatorial pacific where 1 g diagenetic models predict dissolution fluxes larger than observed with benthic flux chambers we conclude that the extent of metabolic caco3 dissolution may vary regionally numerous factors such as the depth of metabolic co2 production and caco3 dissolution kinetics are known or predicted to influence metabolic dissolution among the factors that should be considered in reconciling these observations are l the extent to which sulfate reduction and reoxidation reactions may influence acid base properties in surface sediments and 2 the total sedimentary caco3 content of the sites that may influence porewater acidity through surface exchange reactions at the mineral surface

active diagenetic formation of metal rich layers in n e atlantic sediments sediment cores from the porcupine abyssal plain exhibit an indurated layer 0 5 3 cm thick at depths of approximately 50 cm this is some 15 20 cm below the glacial holocene transition as interpreted by radiocarbon dating and the palaeontological criteria of ruddiman and mcintyre 1981 the layer is forming currently at the oxic post oxic boundary in the sediments as revealed by pore water data o2 and no 3 are present in solution above the layer while fe2 mn2 po3 4 and nh 4 are present in solution below and all these species show concentration gradients indicating fluxes into the layer these data are consistent with the hypothesis for the initiation and sustained formation of such layers proposed by wilsonet al 1986a b the elements mn ni co fe p v cu zn and u are all enriched to varying degrees in the vicinity of the layer some differential stratification of these elements in the vertical consistent with a redox control is observed at one site with a 0 5 cm layer with mn ni and co above fe p v and cu in the layer and u below at another site the metal rich layer has higher fe and p concentrations and is more indurated here all enrichments except co are contained within a single layer sample 3 cm thick

alluvial fan to storm dominated shelf transition in the mesoproterozoic singhora group chattisgarh supergroup central india abstract mesoproterozoic siliciclastic strata at the basal part of the singhora group central india provide an example of a pre vegetation alluvial fan and braid delta depositional system detailed process based facies and paleoenvironmental analysis have led to the identification of 15 facies types grouped under four different facies associations which record paleoenvironmental settings ranging between continental alluvial fan and distal marine shelf two formations investigated are the rehtikhol formation formed in a conglomeratic or coarse arenaceous alluvial fan braid plain and delta setting and the overlying saraipalli formation which preserved the sedimentation record of a storm infested inner to distal shelf setting the preponderance of granular and sandy sediment gravity flow products with subordinate rock fall deposits within the alluvial fan system together with a pervasive west northwesterly paleocurrent is suggestive of a gently sloping beveled source area in the east southeast distal to the inferred fan a braid plain system developed with the decrease in the depositional slope streams within the braid plain had widths up to several hundred meters the braid plain system at the margin of the marine basin developed a delta with the deposition of wave reworked fluvial dominated sediments the crest trends of wave generated bedforms within the inferred delta sediments depict the northeast southwest shoreline interpreted for the singhora sea the prodeltaic basinal part of the singhora braid delta was storm infested the inner shelf acted as a zone of throughput with high velocity storm flows eroding deep narrow scours gutter casts and is interpreted as a zone of bypass operation of geostrophic currents on the singhora shelf has been inferred from the directional relationship of gutters with the inferred orientation of the shoreline a proximal distal relationship has been established within the shelf products based on the relative dominance of erosional and depositional features the singhora alluvial fan and braid delta facies are arranged in a fining upward sequence denudation of the source area increasing bathymetry with relative rise in sea level or a combination of both is inferred both extrabasinal and intrabasinal forcings possibly contributed to the deepening upward trend

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

calcite dissolution in sediments of the ontong java plateau in situ measurements of pore water o2 and ph we present in situ electrode measurements of sediment resistivity pore water oxygen and pore water ph from three stations between 2300 and 3000 m depth on the ontong java plateau in the western equatorial pacific one of these stations is also the site of a concurrent benthic chamber incubation experiment jahnke et al 1994 the pore water oxygen data and a steady state diffusion and reaction model constrain the depth dependent rate of oxic respiration in the sediments and imply a diffusive flux of oxygen to the sediments of 10 21 mol cm 2 yr 1 given these respiration rates the pore water ph data cannot be explained without calcite dissolution driven by metabolically produced co2 the dissolution necessary to explain the observations quantified by a statistical approach is 3 5 6 mol cm 2 yr 1 which corresponds to at least 20 40 of the calcite rain to these sediments over 65 of the total dissolution is driven by metabolic co2 oxygen fluxes and net calcite dissolution constrained by the electrode data are compatible with the benthic chamber measurements of jahnke et al 1994 the dissolution flux while a significant part of the early diagenesis of calcite in these sediments is less than would be predicted by earlier models of dissolution and jahnke et al 1994 probably could not distinguish it from zero with the benthic chamber technique the dissolution rates found in this study are lower than previous estimates because the respiration reaction is concentrated near the sediment water interface and the calcite dissolution rate constants are very small the statistical evaluation of the pore water ph data and model constrain the calcite dissolution rate constant to 0 005 0 16 d 1 following the general trend of lower values determined by in situ techniques rather than by laboratory methods

is burial velocity a master parameter for bioturbation abstract the intensity of biological mixing in a marine sediment is widely believed to be related to the flux of labile organic matter at the same time this flux has been shown to be strongly correlated to the burial velocity one would then expect a significant correlation between biological mixing coefficient d b and burial velocity a nonlinear regression of existing data with a power law eqns 2 and 3 of the text produces a statistically significant correlation the statistical significance of the regression in no way implies causation and in fact it accounts for only about 22 of the total variance in the dataset thus reducing its physical significance a number of additional processes contribute to the large observed variance including timing of mixing events temporal and spatial heterogeneity differences in temporal scales sampling artifacts and specific particle associations with due care the d b relationship may prove useful in defining the likely range of d b values in a particular environment a similar analysis of the tracer identified surface mixed depth shows that it is essentially independent of burial velocity with a worldwide mean of 9 8 4 5 cm depth of mixing is probably more closely related to the energetic costs of deep burrowing

the agglutinated foraminifera from the sw pacific bathyal sediments of the last 550kyr relationship with the deposition of tephra layers abstract the agglutinated foraminiferal content from the last 550 kyr record of the images core md 97 2114 chatham rise new zealand was analysed in order to detect the possible linkage existing between the composition of the grains forming the agglutinated tests and the deposition of tephras the core was collected east of new zealand about 680 km from the active taupo volcanic zone tvz located on the north island thus it contains numerous macro and microscopic tephra layers scanning electron microscopy and energy dispersive spectroscopy analyses were carried out on entire agglutinated foraminifera as well as on sectioned specimens sampled around and within the tephra layers the analyses show that the studied foraminifera built structurally complex tests picking and selecting mineral and biogenic particles on the basis of their availability and abundance in the substratum as well as their composition size and shape in most of the studied species belonging to the order textulariida the composition of the agglutinated grains does not change when the deposition of the tephra layer strongly enriched the substratum in volcanic glass shards only the species karreriella novangliae changed significantly its grain composition mostly selecting volcanic glass fragments to cover the test surface nevertheless the tephra deposition seems to influence the wall microstructure of the agglutinated tests textulariid specimens coming from the volcanoclastic layers have a thinner wall which is also characterised by a less abundant calcareous matrix with respect to the specimens sampled above or below the tephra layer we hypothesise that the volcanic ash deposition probably interfered with the normal agglutinating process by causing the development of more aggressive waters at the sea floor which in turn could have induced carbonate dissolution our observations therefore suggest that the sediment type of the substratum is not the only controlling factor in the construction of the agglutinated foraminiferal test and grain selection which appears to be species dependent

glacial interglacial changes in water mass structure and flow in the sw pacific ocean eight to ten point depth profiles from 1200 to 4800 m water depth of oxygen and carbon isotopic values derived from benthic foraminifera averaged over selected times in the past 160 ka are presented the data are from 10 sediment cores off eastern new zealand mainly north chatham rise this lies under the deep western boundary current in the southwest pacific and is the main point of entry for several water masses into the pacific ocean the benthic isotopic profiles are related to the structure of water masses at present and inferred for the past these have retained a constant structure of lower circumpolar deep water upper circumpolar deep water north pacific deep water antarctic intermediate water with no apparent changes in the depths of water mass boundaries between glacial and interglacial states sortable silt particle size data for four cores are also examined to show that the vigour of the inflow to the pacific while variable appears to have remained fairly constant on average among the lowest last glacial maximum values of benthic 13c in the world ocean 1 03 based on cibicidoides wullerstorfi occurs here at 2200 m comparable values occur in the atlantic sector of the southern ocean while those from the rest of the pacific are distinctly higher confirming that the southern ocean was the source for the unventilated nutrient enriched water seen here oxygen and carbon isotopic data are compatible with a glacial cold deep water mass of high salinity but lower nutrient content or better ventilated below 3500 m depth this contrasts with the south atlantic where unventilated nutrient enriched water extends all the way to the sea bed comparison with previous studies also suggests that the deeper reaches of the antarctic circumpolar current below 3500 m are not homogeneous all around the southern ocean with the kerguelen plateau and or the macquarie balleny ridges posing barriers to the eastward spread of the deepest low 13c water out of the south atlantic in glacials these barriers combined with inferred high density of bottom waters restricted inter basin exchange and allow three glacial domains dominated by bottom waters from weddell sea adelie coast and ross sea to be defined we suggest that the ross sea was the main source of the deep water entering the pacific below 3500 m

onshore offshore correlation of pleistocene rhyolitic eruptions from new zealand implications for tvz eruptive history and paleoenvironmental construction abstract taupo volcanic zone tvz in the north island new zealand is arguably the most active quaternary rhyolitic system in the world numerous and widespread rhyolitic tephra layers sourced from the tvz form valuable chronostratigraphic markers in onshore and offshore sedimentary sequences in deep sea cores from ocean drilling program odp leg 181 sites 1125 1124 1123 and 1122 located east of new zealand ca 100 tephra beds are recognised post dating the plio pleistocene boundary at 1 81 ma these tephras have been dated by a combination of magnetostratigraphy orbitally tuned stable isotope data and isothermal plateau fission track ages the widespread occurrence of ash offshore to the east of new zealand is favoured by the small size of new zealand the explosivity of the mainly plinian and ignimbritic eruptions and the prevailing westerly wind field although some tephras can be directly attributed to known tvz eruptions there are many more tephras represented within odp cores that have yet to be recognised in near source on land sequences this is due to proximal source area erosion and or deep burial as well as the adverse effect of vapour phase alteration and devitrification within near source welded ignimbrites despite these difficulties a number of key deep sea tephras can be reliably correlated to equivalent aged tephra exposed in uplifted marine back arc successions of wanganui basin where an excellent chronology has been developed based on magnetostratigraphy orbitally calibrated sedimentary cycles and isothermal plateau fission track ages on tephra significant pleistocene tephra markers include the kawakawa omataroa rangitawa onepuhi kaukatea kidnappers b potaka unit d ahuroa ongatiti rewa sub rewa pakihikura ototoka and table flat tephras six other tephra layers are correlated between odp core sites but have yet to be recognised within onshore records the identification of pleistocene tvz sourced tephras within the odp record and their correlation to wanganui basin and other onshore sites is a significant advance as it provides 1 an even more detailed history of the tvz than can be currently achieved from the near source record 2 a high resolution tephrochronologic framework for future onshore offshore paleoenvironmental reconstructions and 3 well dated tephra beds correlated from the offshore odp sites with astronomically tuned timescales provide an opportunity to critically evaluate the chronostratigraphic framework for onshore plio pleistocene sedimentary sequences e g wanganui basin cf naish et al 1998 quaternary science reviews 17 695 710

influence of volcanic shards on foraminiferal mg ca in a core from the galapagos region 1 variability in the mg fe al mn and u to ca composition of the planktonic foraminifera g ruber in core tr163 22 an 8 8 m long piston core from just northwest of the galapagos islands reveals distinct patterns of downcore behavior mg ca data follow a general climatic trend with lower values during cold intervals i e marine isotope stages mis 2 4 and higher values during warm intervals i e mis 1 and 5 fe ca and al ca data reveal distinct intervals in which concentrations are elevated tenfold or more over baseline values with highly variable elemental ratios in these intervals the mg ca data are highly correlated with the fe ca and al ca data in these intervals with slopes of 1 13 0 03 and 0 66 0 07 mole mole respectively examination of the sediments from these intervals reveals that they are rich in volcanic debris that is likely derived from galapagos volcanic rocks the presence of small amounts of this volcanic debris can bias shell mg ca to elevated values attempts to use enhanced cleaning to remove the volcanic particles were largely unsuccessful the most successful strategy is to use the fe ca and al ca from the shell digests along with the fe to mg ratio of the volcanic debris to correct the mg ca data for al silicate contamination in which case the corrected data more clearly reveal the primary climatological patterns mn ca and u ca data are characterized by cycles of 20 200 cm length with mn ca having a distinct trend toward higher values between the core top and 200 cm these trends appear to be related to diagenetic coatings on the foraminifera shells most likely in the form of mn carbonates

benthic foraminiferal proxy evidence for the neogene palaeoceanographic history of the southwest pacific east of new zealand abstract canonical correspondence analysis indicates that the distribution of neogene benthic foraminiferal faunas 63 m in seven dsdp and odp sites 500 4500 m water depth east of new zealand 38 51 s 170 e 170 w is most strongly influenced by depth water mass stratification and secondly by age palaeoceanographic changes influencing faunal composition and biotic evolution stratigraphic faunal changes are interpretted in terms of the pulsed sequential development of southern and later northern polar glaciation and consequent cooling of bottom waters increased vertical and lateral stratification of ocean water masses and increased overall and seasonal surface water productivity oligocene initiation of the antarctic circumpolar current and deep western boundary current dwbc flowing northwards past new zealand resulted in extensive hiatuses throughout the southwest pacific some extending through into the miocene planktic foraminiferal fragmentation index values indicate that carbonate dissolution was significant at abyssal depths throughout most of the neogene peaking at upper abyssal depths in the late miocene 11 7 ma with the lysocline progressively deepened thereafter miocene abyssal faunas are dominated by globocassidulina subglobosa and oridorsalis umbonatus with increasing epistominella exigua after 16 ma at upper abyssal depths peak abundances of epistominella umbonifera indicate increased input of cold southern component water to the dwbc at 7 6 ma faunal association changes imply establishment of the modern oxygen minimum zone upper circumpolar deep water in the latest miocene significant latitudinal differences between the benthic foraminiferal faunas at lower bathyal depths indicate the existence of an oceanic front along the chatham rise location of present subtropical front since the early late miocene at least with more pulsed productivity higher e exigua along the south side modern antarctic intermediate water faunal associations were established north of the chatham rise at 10 9 ma and south of it at 3 1 5 ma middle upper bathyal faunas on the campbell plateau are dominated by reticulate bolivinids during the early and middle miocene indicative of sustained productivity above relatively sluggish suboxic bottom waters faunal changes and hiatuses indicate increased current vigour over the campbell plateau from the latest miocene on surface water productivity food supply appears to have increased in three steps at times of enhanced global cooling marked by substantially increased relative abundance of 1 abditodentrix pseudothalmanni alabaminella weddellensis cassidulina norvangi 16 15 ma increased pulsed productivity 2 bulimina marginata f aculeata nonionella auris trifarina angulosa uvigerina peregrina 3 1 5 ma increased overall productivity and 3 cassidulina carinata 1 0 5 ma increased overall productivity three intervals of deep sea benthic foraminiferal taxonomic turnover are recognised 16 15 11 5 10 2 0 5 ma corresponding to intervals of enhanced global cooling and possible productivity changes the late pliocene middle pleistocene extinction associated with increasing northern hemisphere glaciation culminating in the middle pleistocene climatic transition was more significant in the study area than the earlier neogene turnovers

quantifying carbonate dissolution and calibration of foraminiferal dissolution indices in the somali basin two sediment traps moored off somalia in 1992 1993 collected similar settling fluxes of carbonate and siliceous shells formed by various plankton groups planktic foraminifera showed large seasonal variations with more than 74 of the total planktic foraminifera flux collected during the sw monsoon summer upwelling when globigerina bulloides was dominating along with globigerinita glutinata and neogloboquadrina dutertrei the intermonsoon and ne monsoon assemblages were dominated by globigerinoides ruber we used the trap records as our no dissolution reference for comparison with three boxcore recorders in order to quantify the carbonate dissolution along a depth transect dissolution increases downslope from station 905 to 907 and 915 at depths of 1567 m 2807 m and 4035 m respectively the carbonate fraction of the sediment at station 915 which is located near the ccd is the most affected by dissolution with more than 97 of the planktic foraminifera dissolved here the planktic foraminifera assemblage is strongly modified with thick walled species such as n dutertrei globorotalia tumida and pulleniatina obliquiloculata as the most resistant it is not representative of the settling assemblage the planktic foraminiferal assemblages of the sediment surface at stations 905 and 907 remain similar to the trap assemblages and the foraminifera are well preserved although only 25 of foraminifera are apparently preserved at station 905 and 8 at station 907 those numbers are surprisingly low and infer that only a small fraction of the foraminiferal carbonate production is buried and removed from the carbon cycle this discrepancy between the export and buried flux is partly be due to bio mechanical destruction by benthic processes and to supralysoclinal dissolution due to metabolic co2 generated by the benthic organisms another important factor is the interannual variability of the productivity well known in the arabian sea the calibration of commonly used foraminiferal dissolution indices percentage of foraminiferal fragments percentage of resistant species foraminiferal dissolution index fdx to our data only shows reliable results for high dissolution levels 97 off somalia the most accurate of the proxies is the percentage of foraminiferal fragments compared to the other methods tested i e fdx planktic foraminiferal loss l percentage of radiolarians and diatoms percentage of benthic foraminifera the species assemblage appears to be not significantly modified by dissolution unless the estimated shell loss is high 92 of the arriving shells in our samples this level is expressed in the percentage of fragmentation the percentage of radiolarians and diatoms the percentage of resistant foraminifera species and fdx as 80 35 25 and 1 8 respectively the relative abundance of globigerina bulloides is a valid sw monsoon upwelling proxy only when dissolution is moderate 92 globigerina bulloides and globigerinoides ruber have similar burial efficiencies and susceptibilities to dissolution thus the ratio g bulloides g ruber is a valid proxy for past changes in the intensity of the sw monsoon even in the strongly dissolved samples in our sediment record the ratio g bulloides g ruber indicates that the sw monsoon was stronger in the recent past than in 1992 93

calcareous plankton response to orbital and millennial scale climate changes across the middle pleistocene in the western mediterranean abstract the paleoenvironmental conditions through mis 15 9 at the mediterranean ocean drilling program odp site 975 were interpreted by high resolution study of calcareous plankton assemblages compared with available 18o and 13c records and high resolution paleoclimate proxies from the atlantic ocean sea surface temperatures ssts have been estimated from planktonic foraminiferal assemblages using the artificial neural networks method calcareous plankton varied dominantly on a glacial interglacial scale as testified by the sst record foraminiferal diversity total coccolith abundance and changes in warm water calcareous nannofossil taxa a general increase in foraminiferal diversity and of total coccolith abundance is observed during interglacials warmest ssts are reached during mis 11 while mis 12 and mis 10 represent the coldest intervals of the studied record during mis 12 one of the most extreme glacials of the last million years occurrence of globorotalia inflata and of neogloboquadrinids indicates a shoaling of the interface between atlantic inflowing and mediterranean outflowing waters among calcareous nannofossils the distribution of gephyrocapsa margereli gephyrocapsa muellerae 4 m also supports a reduced atlantic mediterranean exchange during mis 12 superimposed on glacial interglacial variability six short term coolings are recognized during mis 12 and 10 which appear comparable in their distribution and amplitude to the heinrich type events documented in the atlantic ocean in the same interval during these h type events neogloboquadrina pachyderma s and g margereli g muellerae 4 m increase as a response to the enhanced inflow of cold atlantic water into the mediterranean via the strait of gibraltar mediterranean surface water hydrography appears to have been most severely affected at termination v during the h type event ht4 possibly as a response to a large volume of atlantic meltwater inflow via the strait of gibraltar and or to freshwater terrigenous input deriving from local mountain glaciers three additional sst coolings are recorded through mis 14 16 but these are not well correlated with heinrich type events documented in the atlantic ocean in the same interval during these cooling episodes only the subpolar turborotalita quinqueloba increases these results highlight the sensitive response of the mediterranean basin to millennial scale climate variations related to northern hemisphere ice sheet instability and support the hypothesis that the tight connection between high latitude climate dynamics and mediterranean sea surface water features can be traced through the middle pleistocene

subduction zone volcanic ash can fertilize the surface ocean and stimulate phytoplankton growth evidence from biogeochemical experiments and satellite data volcanoes confront earth scientists with new fundamental questions can airborne volcanic ash release nutrients on contact with seawater thereby excite the marine primary productivity mpp and most notably can volcanoes through oceanic fertilization affect the global climate in a way that is so far poorly understood here we present results from biogeochemical experiments showing that 1 volcanic ash from subduction zone volcanoes rapidly release an array of nutrients co limiting algal growth in vast oceanic areas 2 at a speed much faster minute scale than hitherto known and that marine phytoplankton from low iron oceanic areas can swiftly within days utilize iron from volcanic sources we further present satellite data possibly indicating an increase of the mpp due to the seaward deposition of volcanic particulate matter our study supports the hypothesis that oceanic iron fertilization with volcanic ash may play a vital role for the development of the global climate

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

authigenic seep carbonates cementing coarse grained deposits in a fan delta depositional system middle miocene marnoso arenacea formation central italy seep carbonates 13 c depleted are present at different levels within the miocene terrigenous succession of deruta marnoso arenacea formation central italy they are associated with pebbly sandstones and conglomerates in a tectonically active fan delta slope depositional system most of these seepcarbonates are included in slide slump horizons as scattered blocks the occurrence of seep carbonates is clear evidence of the flow of methane rich fluids pervading the sediments fluids probably of biogenic origin may have reached the sea bottom through thrust faults and selectively infiltrated the more permeable coarse grained horizons deposited along the slope different stages of fluid emissions are documented slow flux stage corresponding to the development of large carbonate bodies and dense chemosynthetic communities and fast fluid flow associated with intense carbonate brecciation pipes and veins large amounts of authigenic carbonates are reworked by slope failures triggered by tectonics and fluids reducing sediment strength in situ cementation of slide blocks may also have occurred due to remobilization of methane rich fluids by mass wasting processes

pleistocene biogeochemical record in the south west pacific ocean images site md97 2114 chatham rise through a multidisciplinary approach based on novel micropaleontological and geochemical analyses the main paleoceanographic and paleoclimate changes that have influenced the surface and deep water circulation in the sw pacific ocean chatham rise eastern new zealand during the last million years are reconstructed this region represents a key area for investigating the climate evolution during the pleistocene because here the largely wind driven antarctic circumpolar current interacts with the west pacific ocean circulation via the deep western boundary current the major source of deep water for the whole pacific ocean to understand coupling or decoupling events between sea surface and bottom waters a continuous marine sedimentary succession since 1 1 ma recovered by the images international marine past global change study cruise in the sw pacific ocean core md97 2114 has been investigated based on calcareous planktonic and benthic microfossil content and c and o isotope record performed on planktonic and benthic foraminiferal tests results show the occurrence of long and short term patterns of climate and ocean circulation in the last million years as the result of the interplay of ice sheet dynamics surface tropical versus polar water inflow and trophic status of the surface water copyright 2012 john wiley sons ltd

explosive volcanism as a cause for mass mortality of pteropods recently it has been proposed that anthropogenic co2 emissions may affect marine ecosystems by causing ocean acidification in particular it is suggested that within acidified waters calcifying organisms would be subject to malformation and enhanced dissolution here we present evidence suggesting that this process occurs naturally where explosive volcanism deposits ash directly into ocean surface waters sediment cores from around the island of montserrat lesser antilles volcanic arc contain distinct horizons of planktic fauna associated with recently deposited volcanic ash layers from the soufriere hills volcano within these layers are abundant thecosome pteropod shells that display evidence of partial dissolution and etching of their aragonitic shells and appear to have suffered mass mortality during large eruptions from the volcano laboratory studies show that the acids bound to ash surfaces from the 2003 volcanic dome collapse event of the soufriere hills volcano could have caused the upper 5 m of the water column to become undersaturated with respect to aragonite when combined with the large fluxes of acidic aerosols principally as so2 from the volcano during eruptions it is proposed that volcanogenic ocean acidification by marine ash falls is a significant contributing factor to these observed mass mortality events

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

bias in the paleoceanographic time series tests with a numerical model of u corg and al burial 1 we have constructed a nonsteady state numerical model of organic carbon aluminum and uranium burial to examine the dynamic response of sediments to variations on thousand years scale the three components are defined by distinct behaviors in the sedimentary system the aluminum is a conservative component the organic carbon is a nonconservative component degraded in superficial sediment and the uranium is a component affected by redox conditions by introducing a simultaneous variation of incoming fluxes of corg and al geochemical profiles of al corg and u clearly show separate distributions after burial each component record the synchronous variation of the incoming fluxes but the position in the sedimentary pile of the recording differs from a component to another we show that a minimum of u could be linked to a rapid ascent of the oxic front during an increase in corg flux

onset of pacific style deep sea sedimentary carbonate cycles at the mid pleistocene transition the calcium carbonate caco3 content of deep sea sediments in the pacific ocean increases during glacials of the late pleistocene in comparison to interglacials whereas records of sedimentary caco3 in the atlantic ocean show an anticorrelated pattern across glacial interglacial cycles here we show that this anticorrelation in inter ocean caco3 cycles arose comparatively recently at 1 10 million years ago ma during the mid pleistocene transition before this time we show that the caco3 content of pacific and atlantic ocean sediments experienced in phase cyclicity both having atlantic style phasing with respect to glacial interglacial cycles the onset of anticorrelated cyclicity at 1 10 ma involved a twofold switch in the pacific s caco3 cycles glacial caco3 preservation became consistently better while interglacial preservation became consistently worse we demonstrate that the cause of this glacial interglacial mirror imaging of pacific caco3 dissolution cyclicity at 1 10 ma was a switching over of the relative ventilation state of abyssal south pacific waters between glacials and interglacials specifically we suggest that a consistent strengthening of deep water ventilation within the pacific sector of the southern ocean during glacials drove glacial pacific caco3 dissolution to diminish while a contemporaneous weakening of very well ventilated upstream north atlantic deep water during interglacials drove interglacial pacific caco3 dissolution downstream to intensify we propose that the increased mean alkalinity of the global deep ocean driven by the geographically and bathymetrically vast pacific ocean during glacials after 1 10 ma may explain part of the drawdown in glacial atmospheric co2 levels hypothesised to have been linked to the increased severity of these late pleistocene glacials

authigenic cadmium enrichments in suboxic sediments precipitation and postdepositional mobility the postdepositional mobility of cd and u has been investigated in north atlantic turbidites in order to validate their utility as proxies of paleo organic carbon fluxes in this region pelagic sediments are interspersed with relatively organic rich turbidites following instantaneous emplacement of turbidite units an oxidation front progressively migrated downwards into the suboxic turbidite thereby leading to redistribution of authigenic phases according to their affinity to different redox conditions authigenic cd concentrations show a large peak at the redox boundary and are significantly lower in the oxidized portion than in the deeper unoxidized part of the turbidite this distribution indicates that cd has been continuously remobilized by the oxidation front thereby suggesting high sensitivity of the cd species to the redox state and an efficient immobilization mechanism for cd under reducing conditions we propose the precipitation of cds as a plausible mechanism for removal of cd in reducing sediments rather than adsorption onto mineral surfaces this proposal is consistent with porewater data indicating diffusion of cd toward and uptake by suboxic sediments solubility calculations suggest that precipitation of cds may occur in suboxic sediments in the presence of trace levels of h2s below routine detection limits there is no evidence for release of cd or u back into seawater upon oxidation of reducing sediments the strong coupling between precipitation of authigenic cd and u and the early diagenetic degradation of organic carbon offers the potential of reconstructing paleo productivity using records of cd and u however postdepositional redistribution of authigenic cd and u may significantly alter records of authigenic cd and u thereby rendering paleo productivity reconstructions uncertain we propose that the cd u authigenic ratio may provide a qualitative indicator to assess the relative role of steady state incorporation relative to transient burn down enrichments

concentration oxidation state and particulate flux of uranium in the black sea abstract in contrast to its unreactive behavior in the open ocean uranium is removed from seawater to sediments of anoxic marine basins four biogeochemical processes have been proposed to account for this removal active uptake by organisms whose remains are preserved by the anoxic conditions of the sediments complexation of u vi by particulate organic matter chemical reduction of soluble u vi to insoluble u iv which is scavenged to the sediments by settling particles and precipitation of uranium within the sediments themselves the black sea is the largest anoxic marine basin in the world today waters below 150 200 m are anoxic and h2s levels build up to about 400 mol 1 1 in the bottom water maximum depth 2200 m concentrations of total u and the oxidation state of dissolved u were measured throughout the water column while particulate u fluxes were determined from time series sediment trap samples collected in the deep anoxic zone bottom waters were depleted in u by 40 relative to the initial u content of the water two independent methods gave residence times of dissolved u in the deep water column of about 103 years uranium occurred throughout the water column as soluble chemically labile reducible u vi rather than the thermodynamically favored u iv uranium is neither reduced to u iv by the high levels of h2s nor is it rapidly scavenged from the water column as would be expected for strongly hydrolyzed tetravalent actinides like u iv fluxes of particulate authigenic u measured with sediment traps are at least two orders of magnitude less than the rate of authigenic u burial in black sea sediments therefore the first three processes listed above contribute negligibly to the deposition of u in the sediments of anoxic marine basins such as the black sea the dominant removal process must involve precipitation of u in the sediments rather than scavenging from the water column

early diagenetic processes in the muddy sediments of the bay of biscay abstract in order to understand the early diagenesis processes occurring in continental margin environment modern sediments collected in six different sites from the bay of biscay have been studied these sites can be separated into two groups in the shallowest stations where sediments are highly bioturbated organic carbon levels are higher than 2 in the deepest stations sediments are much less bioturbated and organic carbon levels are lower in all sites the vertical distribution of redox sensitive species can be explained by the well established depth sequence of redox reactions based on the bacterially mediated oxidation of organic matter we have considered some alternative reaction pathways to explain the profiles of fe mn and n species these reactions deal with the ammonia oxidation by manganese oxide the aerobic denitrification and the oxidation of dissolved iron ii by nitrate or mn oxides vertical flux calculations with a simple diffusion model indicate that these reactions could account for the reduction of all the mn oxides and the oxidation of all the upward diffusing fe ii they may also be responsible for a significant part of the total dinitrogen production the relative importance of these pathways on early diagenetic processes and benthic fluxes has not been determined and must be examined with additional experimental works our study suggests however that the coupling between the benthic cycles of iron manganese and nitrogen could strongly influence the carbon cycling at the ocean floor

diagenetic separation of cadmium and manganese in suboxic continental margin sediments abstract the vertical distribution of cd differs from that of mn in sediment cores taken from the continental margins of the arctic and atlantic oceans the oxic surface sediment is depleted in cd and enriched in mn whereas the subsurface sediment is enriched in cd and depleted in mn in some cores the distributions of solid phase and dissolved mn are offset the porewater profiles indicate that mn is being precipitated relatively deep in the sediment whereas the solid phase distributions indicate that mn has been precipitated very close to the sediment surface in the recent past at one deep site located near the base of the continental slope 3000 m the offset may be caused by a relatively recent decrease in ocean productivity a corresponding decrease in the organic carbon flux to the sediment and a subsequent migration of the redox boundary deeper into the sediment however at a site where the upper sediment layers have accumulated during the last few decades this explanation cannot account for the offset distributions we propose that a fluctuating input of organic matter to the sediment on seasonal or decadal timescales causes the position of the redox boundary to fluctuate the fluctuating redox boundary pumps dissolved mn upward and concentrates it as mn oxide in a distinct layer at the upper limit of the redox excursion at the same time it pumps cd downward and concentrates it in a distinct layer at the lower limit of the redox excursion the net result of a fluctuating redox boundary is to increase the spatial separation of cd and mn during the early diagenesis of suboxic sediments

when deep diagenesis in arctic ocean sediments compromises manganese based geochronology abstract we used a diagenetic model to test the hypothesis that manganese rich layers in gas hydrate bearing arctic ocean sediments are reliable time markers for interglacial periods in the model diagenesis is fuelled by two sources of reactive carbon particulate organic carbon settling to the sediment surface and methane diffusing up from deep gas hydrate deposits the model includes oxidation of organic carbon and soluble reduced manganese by oxygen supplied continuously from an invariant bottom water oxygen reservoir reduction of particulate manganese by hydrogen sulfide generated through anaerobic methane oxidation transport of dissolved oxygen and manganese by diffusion and advective transport of particulate components by burial particulate organic matter and particulate manganese are only supplied to the sediment during interglacials sulfate reduction is not modeled explicitly instead the effect of anaerobic methane oxidation on mn reduction is simulated at the lower boundary of the model by prescribing that particulate manganese is reduced there to soluble mn ii the soluble reduced mn then diffuses upward and is oxidatively precipitated to mn iv by downward diffusing oxygen the upward flux of soluble mn ii is thus a function of the rate at which particulate manganese is advected into the mn reduction layer at the bottom of the model it is not synchronous with events at the sediment water interface model runs reveal that under idealized but realistic conditions for the arctic ocean oxidation of upward diffusing mn ii generates post depositional manganese enrichments that cannot readily be distinguished from the manganese rich sediment layers that accumulate during interglacials this compromises the use of manganese rich layers as proxies for interglacial periods in contrast manganese rich layers may be used as first order markers of interglacial periods in sediments where gas hydrates or other forms of reactive carbon are absent

development of sediment drifts approaching an active plate margin under the sw pacific deep western boundary current the abyssal pacific ocean is fed by a 1000 km wide deep western boundary current dwbc that flows northward along the continental margin east of new zealand between the passive margin of chatham rise and the subduction zone of kermadec trench a distance of 1200 km the dwbc has formed a suite of sediment drifts over a depth range of 2200 5700 m airgun and 3 5 khz profiles record a variety of drift types that reflect regional variations in bathymetry sediment supply and the tectonic volcanic framework on chatham rise the dwbc has deposited a sinuous linear body along the south flank 3000 m an extensive apronlike drift on the north flank 2200 4500 m and a ridgelike drift about the rise base 4500 5200 m the flow has also deposited a body of sediment over 400 km long within a moat at the base of the nearby louisville seamount chain further downcurrent the 250 km long rekohu drift 3600 4190 m has developed northward to 39 s south of this latitude drifts comprise mainly reworked pelagic hemipelagic material and sediment transported from distant southerly sources in contrast drifts north of 39 s have received a major injection of terrigenous sediment from hikurangi channel which runs 1400 km from new zealand eastward across the hikurangi plateau to disgorge on to the abyssal floor at the plateau edge en route turbidity current overspill from the channel has moved north under the influence of the shallow dwbc to contribute to a series of small ridge and patch drifts among the numerous seamounts on the plateau at 3500 4200 m off hikurangi channel mouth a large fan has accumulated the dwbc has extended the fan into a drift running over 250 km along the base of hikurangi plateau 5150 5770 m toward kermadec trench here drift sediment becomes increasingly disrupted by mass wasting associated with the active subduction in this area the seismic stratigraphy reveals the drifts to rest mainly on a widespread erosional surface that is interpreted to mark the inception of the dwbc in the region with the late oligocene opening of the australian antarctic seaway drift construction commenced during the miocene but was punctuated in the late miocene by another period of erosion that coincided with increased bottom water production in antarctica deposition resumed in plio pleistocene times when large quantities of sediment from the rapidly rising landmass of new zealand were injected into the boundary current the modern flow continues to affect drift deposition as manifest by an active boundary channel along the foot of hikurangi plateau and widespread scour zones and sediment wave fields

bioevents and redox conditions around the cenomanian turonian anoxic event in central mexico abstract the xilitla section of central mexico western margin of the proto north atlantic is characterized by pelagic sediments enriched in marine organic matter using biostratigraphic and radiometric data it was dated at the latest cenomanian earliest turonian transition we identified an interval coeval with the faunal turnover associated with the oceanic anoxic event 2 oae 2 recording the heterohelix shift and the filament event for the first time in mexico an integral analysis of sedimentary facies pyrite and geochemical proxies reveals vertically variable redox conditions with prevailing anoxic to dysoxic bottom waters along with phosphorous and manganese depletion the highest content of total organic carbon and of certain redox sensitive trace elements rstes is found during part of the anoxic event confirming more uniform and constant oxygen depleted conditions this interval is also characterized by a significant enrichment in biogenic barium and elevated toc ntot ratios suggesting a link between productivity and anoxia sulfur isotope fractionation has a maximum value within the anoxic event favored by the increase in the flux of organic matter and intensified through sulfur recycling highly bioturbated beds representing short lived episodes of oxic conditions are intermittent within the oae 2 and become more frequent in the early turonian this study proposes a model similar to that of modern upwelling regions high marine productivity controlled organic matter burial and oxygenation at the seafloor varying between anoxic laminated facies with small pyrite framboids and dysoxic conditions bedding parallel bioturbated facies with inoceramid bivalves and large pyrite framboids interrupted by short term well oxygenated episodes thoroughly bioturbated facies with common benthic foraminifera general low oxygen conditions led to the formation of glauconite and pyrite bacterially mediated the enrichment of redox sensitive trace elements in sediments cd zn v and cr scavenged by organic matter and ni mo pb co and re by pyrite and resulted in mn and p depletion

rhenium in the black sea comparison with molybdenum and uranium rhenium concentrations were measured in the black sea to determine the behavior of this redox sensitive element in an anoxic basin under reducing conditions re is removed from solution leading to its depletion from black sea deep waters compared with uranium water column re and mo profiles show evidence of removal from mid depths suggesting that these elements are scavenged either in the water column or slope sediments to a greater degree than u black sea surface waters are enriched in re reflecting re in rivers draining into the northern black sea that are enhanced up to 80 fold over other large world rivers this enrichment is most likely anthropogenic and may be due to coal burning in the region a simple two box model is used to demonstrate that re concentrations in the black sea are not in steady state with respect to current riverine inputs and authigenic fluxes riverine inputs of u and mo are not as significant perhaps reflecting the fractionation of re from the other elements during a high temperature combustion process re2o7 is volatile above 270 c

carbon isotope evidence for changes in antarctic intermediate water circulation and ocean ventilation in the southwest pacific during the last deglaciation 1 deep sea sediment core fr1 97 gc 12 is located 990 mbsl in the northern tasman sea southwest pacific where antarctic intermediate water aaiw presently impinges the continental slope of the southern great barrier reef analysis of carbon 13c and oxygen 18o isotope ratios on a suite of planktonic and benthic foraminifera reveals rapid changes in surface and intermediate water circulation over the last 30 kyr during the last glacial maximum there was a large 13c offset 1 1 between the surface dwelling planktonic foraminifera and benthic species living within the aaiw in contrast during the last deglaciation termination 1 the 13cplanktonic benthic offset reduced to 0 4 prior to an intermediate offset 0 7 during the holocene we suggest that variations in the dominance and direction of aaiw circulation in the tasman sea and increased oceanic ventilation can account for the rapid change in the water column 13cplanktonic benthic offset during the glacial interglacial transition our results support the hypothesis that intermediate water plays an important role in propagating climatic changes from the polar regions to the tropics in this case climatic variations in the southern hemisphere may have led to the rapid ventilation of deep water and aaiw during termination 1 which contributed to the postglacial rise in atmospheric co2

carbonate preservation in marine sediments mid to higher latitude quantitative proxies 1 observations of carbonate preservation in marine sediments have long been used to infer changes in ocean circulation or biogenic production when combined with measures of organic carbon rain and calcite accumulation rates quantitative estimates of changes in preservation can reveal variation in biogenic fluxes the org c to calcite flux ratio and saturation state of bottom waters here we develop quantitative dissolution proxies for mid to higher latitudes based on foraminiferal test fragmentation examining surface sediments we find that fragmentation in g bulloides and g truncatulinoides is linear with increasing seabed dissolution rate and can be used to quantify changes in carbonate preservation g truncatulinoides shows a constant relationship of fragmentation to dissolution however we observe that although linear to dissolution rate the fragmentation in g bulloides depends on which morphotype is present other species such as g inflata have complex responses to increasing dissolution and are less direct preservation indicators

response of calcareous nannofossil assemblages to paleoenvironmental changes through the mid pleistocene revolution at site 1090 southern ocean abstract quantitative study on calcareous nannofossil assemblages has been performed in high time resolution 2 3 kyr at the ocean drilling program site 1090 the location of this site in the southern ocean is crucial for the comprehension of thermohaline circulation and frontal boundary dynamics and for testing the employ of nannoflora as paleoceanographical tool the chronologically well constrained investigated record spans between marine isotope stage mis 35 and 15 through an interval of global paleoclimate and paleoceanographical modification also known as mid pleistocene revolution mpr measures of ecological shannon weaver diversity and paleoproductivity and dissolution indices together with spectral and wavelet analyses carried out on the acquired time series provide valuable information for interpretation of data in terms of paleoecology and paleoceanography assemblages are mainly represented by dominant small gephyrocapsa common calcidiscus leptoporus s l coccolithus pelagicus s l gephyrocapsa 4 5 5 m the extinct pseudoemiliania lacunosa and reticulofenestra spp r asanoi and reticulofenestra sp morphotypes discriminated within calcidiscus leptoporus s l and coccolithus pelagicus s l reveal that they may have had different ecological preferences during pleistocene with respect to the present the composition and fluctuation in nannofossil assemblage and their comparison with the available sea surface temperature sst and c org curves suggest a primary ecological response to paleoenvironmental changes relationships to different surface water features and boundary dynamics as well as to different efficiencies and motions of the intermediate and deep water masses have been inferred a more northward position of subantarctic front saf during most of the early pleistocene record has been highlighted based on assemblage composition characterised by common calcidiscus leptoporus s l coccolithus pelagicus s l medium gephyrocapsa 4 5 5 m and by the rarity or absence of umbilicosphaera spp rhabdosphaera spp pontosphaera spp oolithotus fragilis exceptions are the more intense interglacials mis 31 17 and probably mis 15 when a southward displacement of frontal system occurred coincident with peaks in abundance of helicosphaera spp and syracosphaera spp higher nutrient content and more dynamic conditions occurred between mis 32 and mis 25 in relation to shallower location of nutrient rich antarctic intermediate water aaiw core and to reduction of glacial interglacial variability a nannofossil barren interval is coincident with the known stagnation of south atlantic deep water circulation during mis 24 when north atlantic deep water nadw was reduced or suppressed and an enhanced northward deep penetration of the more corrosive circumpolar deep water cpdw took place an event of strong instability in nutricline dynamics characterised the transition mis 23 22 as suggested by sharp fluctuations in paleoproductivity proxies linked to major changes in oceanographic circulation and to the first distinct increase of larger ice volumes at this time from mis 21 upward the nannofossil variations seem to be primarily controlled by glacial interglacial cyclicity and temperature fluctuations the cyclic fluctuation recognised in nannofossil abundance seems to be linked to orbitally forced climatic variation primarily to the obliquity periodicity recorded in the patterns of c leptoporus intermediate 5 8 m and c pelagicus pelagicus 6 10 m however no obvious and linear relations may be always observed between nannoflora fluctuation and milankovitch parameters suggesting more complex and unclear relationships between nannofossils and environmental change

pleistocene carbonate dissolution fluctuations in the eastern equatorial pacific on glacial timescales evidence from odp hole 1241 abstract this study presents a record of dissolution from the eastern equatorial pacific eep that extends to 2 1 ma based on sediments from ocean drilling program odp site 1241 a new benthic oxygen isotope record was developed in order to provide the stratigraphic framework for the pleistocene section of the core the isotope record extends back to 2 1 ma covering mis 1 80 and has a sampling resolution of 2 kyr from 0 to 360 kyr and 5 kyr from 360 to 2100 kyr dissolution at odp site 1241 is characterized through the use of percent coarse fraction cf and shell fragmentation records these records indicate that cf in the eep is recording a dissolution signal dominated by the 41 kyr and 100 kyr climate cycles and that preservation maxima lag glacial maxima by 9 14 kyr at the major orbital periods the dissolution signals observed in the odp site 1241 record can be correlated across the pacific and likely record the response to basinwide changes in carbonate chemistry the dissolution fluctuations and 13c signal observed at odp site 1241 are consistent with both the shackleton 1977 toggweiler et al 2006 hypotheses that explain changes in the global carbon cycle during glacial interglacial transitions

effects of oceanic circulation and volcanic ash fall on calcite dissolution in bathyal sediments from the sw pacific ocean over the last 550 ka abstract the effects on calcite dissolution of both oceanic circulation and volcanic ash fall were evaluated in lower bathyal sediments over the last 550 ka record from core md 97 2114 recovered on the northern slope depth of 1936 m in the pacific deep water pdw of the chatham rise east of new zealand sw pacific ocean this area has been impacted by changes in glacial interglacial circulation and ocean chemistry as well as by the explosive volcanic activity of the taupo volcanic zone several micro paleontological dissolution proxies based on planktonic foraminifera and calcareous nannofossils were analysed in order to evaluate the calcite dissolution of the deep sea sediments these were compared with a couple of proxies of primary productivity benthic foraminiferal epifaunal infaunal ratio and 13cbenthic foraminifera and the abundance of volcanic glass the dissolution proxy data from md 97 2114 were compared with two nearby odp sites odp 1123 3290 m deep bathed by the lower circumpolar deep water lcdw and odp 1125 1365 m deep bathed by the antarctic intermediate water aaiw the results suggest 1 the calcite dissolution preservation cycles at all three core sites show glacial interglacial g i periodicities that match the previously described pacific style caco3 cycles 2 several short term dissolution events do not follow this general scheme and occur following tephra deposition the dissolution related to the tephra deposition seems to have mostly affected calcareous nannofossils thus we hypothesise that the ash fall induced a temporary reduction of the surface water ph below 7 8 which affected the coccolithophores that inhabit the surface waters 3 other short term dissolution events 1000 years are unrelated to tephra deposition and are possibly driven by the slowing of deep sea circulation and a reduced deep western boundary current dwbc this lead to the dominance of older more corrosive pacific deep water pdw flowing in to the region resulting in coeval dissolution episodes at all three core sites depth range from 1365 to 3290 m

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

reconstructing the quaternary evolution of the world s most active silicic volcanic system insights from an 1 65 ma deep ocean tephra record sourced from taupo volcanic zone new zealand abstract the taupo volcanic zone tvz central north island new zealand is the most frequently active quaternary rhyolitic system in the world silicic tephras recovered from ocean drilling programme site 1123 41 47 16 s 171 29 94 w 3290 m water depth in the southwest pacific ocean provide a well dated record of explosive tvz volcanism since 1 65 ma we present major minor and trace element data for 70 quaternary tephra layers from site 1123 determined by electron probe microanalysis 1314 analyses and laser ablation inductively coupled plasma mass spectrometry 654 analyses trace element data allow for the discrimination of different tephras with similar major element chemistries and the establishment of isochronous tie lines between three sediment cores 1123a 1123b and 1123c recovered from site 1123 these tephra tie lines are used to evaluate the stratigraphy and orbitally tuned stable isotope age model of the site 1123 composite record trace element fingerprinting of tephras identifies 4 5 m and 7 9 m thick sections of repeated sediments in 1123a 49 0 53 5 mbsf metres below seafloor and 1123c 48 1 56 0 mbsf respectively these previously unrecognised repeated sections have resulted in significant errors in the site 1123 composite stratigraphy and age model for the interval 1 15 1 38 ma and can explain the poor correspondence between 18o profiles for site 1123 and site 849 equatorial pacific during this interval the revised composite stratigraphy for site 1123 shows that the 70 tephra layers when correlated between cores correspond to 37 38 individual eruptive events tephras 7 of which can be correlated to onshore tvz deposits the frequency of large volume tvz derived silicic eruptions as recorded by the deposition of tephras at site 1123 has not been uniform through time rather it has been typified by short periods 25 50 ka of intense activity bracketed by longer periods 100 130 ka of quiescence the most active period at least 1 event per 7 ka occurred between 1 53 and 1 66 ma corresponding to the first 130 ka of tvz rhyolitic magmatism since 1 2 ma 80 of tephras preserved at site 1123 and the more proximal site 1124 were erupted and deposited during glacial periods this feature may reflect either enhanced atmospheric transport of volcanic ash to these sites up to 1000 km from source during glacial conditions or more speculatively that these events are triggered by changes in crustal stress accumulation associated with large amplitude sea level changes only 8 of the 37 38 site 1123 tephra units 20 can be found in all three cores and 22 tephra units 60 are only present in one of the three cores whether a tephra is preserved in all three cores does not have any direct relationship to eruptive volume instead it is postulated that tephra preservation at site 1123 is patchy and influenced by the vigorous nature of their deposition to the deep ocean floor as vertical density currents at this site at least 5 cores would need to have been drilled within a proximity of 10 s to 100 s of metres of each other to yield a 99 chance of recovering all the silicic tephras deposited on the ocean surface above it in the past 1 65 ma

evaluation of the caco3 dissolution proxies in sediment cores from above the lysocline calcium carbonate analyses were carried out from two size fractions 63 m from the ocean drilling program sites 752 and 715 collected from above the lysocline depth in the indian ocean to evaluate the calcium carbonate size index as paleocarbonate ion proxy in these cores size index values varied from 69 to 81 at site 752 and showed a similar pattern with that of total carbonate content at this site but high values of size index and the location of this site far from any landmass suggest that only changes in productivity of overlying waters are responsible for the observed variations low values of size index at site 715 suggest supralysoclinal dissolution the inverse relation between size index variations and the total caco3 content shows that the total carbonate variations are controlled by the finer fraction composed of juvenile foraminifera foraminifera fragments and coccolithophores this further confirms the observed variations of caco3 content of the 63 m fraction which follows the trend of total caco3 content this study demonstrates that apart from factors such as breakup of shells after burial due to organic matter respiration and dilution due to terrigenous material changes in surface water productivity and coccolithophores might be a constraint to use size index as a paleocarbonate ion proxy for sediments from above the lysocline

a 36 kyr geochemical record from the sea of japan of organic matter flux variations and changes in intermediate water oxygen concentrations intervals of organic c and carbonate rich laminated sediments occur in the sea of japan with roughly the same frequency as temperature changes observed in greenland ice cores providing clear evidence of rapid oceanographic change during the past 36 kyr planktonic foraminiferal 18o data suggest that only the laminated sediments deposited during the last glacial maximum lgm and perhaps one other interval formed during a period of increased water column stratification sedimentary re and mo data are consistent with bottom waters that were sulfidic during the lgm and suboxic during other laminated intervals results of a numerical model of corg and re burial are consistent with a mechanism whereby an increased corg flux to the seafloor drove oxygen concentrations toward depletion during times of deposition of the suboxic laminated intervals such a process could have resulted from increased upwelling driven either by increased deep water formation due to colder and or more saline surface waters or by stronger northeasterly monsoonal winds

planktic foraminiferal dissolution in the twilight zone abstract calcite dissolution of planktic foraminifers that settle from the surface ocean to depths has been assessed using the weight size relationship of tests and correlated to carbonate ion concentration co 3 2 of ambient sea water globigerina bulloides and globigerinita glutinata were sampled from the north atlantic and the arabian sea during different seasons spring and fall and the monsoons respectively test weight has been determined for single tests from narrow size classes 250 8 m and 300 7 m minimum test diameter initial test weight of both species in surface waters differs between regions and seasons weight loss of settling tests in the twilight zone between 100 and 1000 m water depths averaged 19 below the twilight zone 1000 2500 m no weight loss occurs on average and tests may even gain weight remineralization of settling planktic foraminiferal tests is most pronounced at maximum co 3 2 accordingly strong dissolution occurs in the twilight zone at the depth of maximum decrease in co 3 2 it is assumed that dissolution of planktic foraminiferal calcite is caused by co 3 2 under saturation inside the test buffered by diffusive exchange of co 3 2 ions with the ambient sea water through the pores and aperture consequently reconstruction of small scale differences in seawater co 3 2 from test weight alone is not feasible and systematic correlation between test weight and co 3 2 of the ambient sea water is statistically not significant at constant co 3 2 remineralization cannot be deduced from test weight neither at high nor low co 3 2 saturation in total our data suggest that the global vertical planktic foraminiferal caco 3 flux is about 19 lower than calculated by schiebel 2002 planktic foraminiferal sedimentation and the marine calcite budget global biogeochemical cycles 16 4 1065 doi 10 1029 2001gb001459

calcareous plankton and geochemistry from the odp site 1209b in the nw pacific ocean shatsky rise new data to interpret calcite dissolution and paleoproductivity changes of the last 450 ka abstract the high resolution multi proxy investigation of microfossil and isotopic data from shatsky rise odp site 1209b nw pacific ocean is presented to evaluate the potential of calcareous nannofossil assemblages as dissolution and paleoproductivity proxies over the last 450 ka to identify the best nannofossil index to evaluate dissolution in particular under polarized light microscope we calculate and compare the different nannofossil and planktonic foraminiferal dissolution indices from our original dataset the results demonstrate that the most reliable and reproducible nannofossil dissolution index is the nannofossil dissolution index ndi proposed by marino et al 2009 particularly for records prior to 250 ka the ndi data from the studied site 1209b represent evidence of preservation maxima mainly during deglaciations whereas dissolution peaks are recorded at the onset of glacial phases or during severe interglacials these fluctuations are demonstrated to be basin wide features in the pacific the synchronous timing in the fluctuations of the preservation indices which consistently lagged behind the oxygen isotope cycles clearly demonstrates the basin wide changes in the ocean chemistry during the glacial interglacial transitions the mid brunhes dissolution event which was recorded in the western pacific at depths below the lysocline at the marine isotope stage mis 11 is not detectable at our relatively shallower site at the studied site the intervals of high productivity generally coincide with the time of good preservation and light carbon isotope values and vice versa therefore carbonate undersaturation and changes in ocean chemistry carbonate ion concentration rather than the variations in the organic carbon flux appear to have controlled the pattern of caco3 preservation in addition to the characterization of the dissolution proxies changes in the calcareous nannofossil assemblages were used to evaluate the primary productivity fluctuations at the mid latitudes of the nw pacific over the last 450 ka the results highlight a general decrease of paleoproductivity during the entire time period as well as shorter glacial interglacial fluctuations from the base core upwards we interpret these features to be variations in the thermocline and nutricline dynamics related to the northward migration of the kuroshio extension which was triggered by the mid brunhes event and may have caused deepening of the thermocline nutricline at the site the spectral and wavelet analyses performed on the microfossil database prove that the variations in paleoproductivity and carbonate dissolution over the last 450 ka were primarily driven by the glacial interglacial variability 100 ka periodicity and by the obliquity controlled changes

toward better paleocarbonate ion reconstructions new insights regarding the caco3 size index 1 the reconstruction of paleocarbonate ion concentrations provides an important constraint on the contribution of the caco3 cycle to the decrease in atmospheric co2 content during glacial time such reconstructions have been challenging because each of the existing paleo co32 indices has serious limitations in this study we reexamine the broecker clark caco3 size index by analyzing the 20 m 20 to 38 m and 38 to 63 m fractions in sediments from the ontong java plateau and the ceara rise scanning electron microscope analyses demonstrate that the less than 20 m caco3 is dominated by coccoliths and the greater than 20 m caco3 is dominated by foraminifera our results clearly indicate that the coccoliths are far more resistant to dissolution than the foraminifera referenced to a core top sample from 2 31 km depth in a core top sample from 4 04 km depth on the ontong java plateau 70 of the foraminifera caco3 was dissolved as opposed to only 7 of the coccolith caco3 we found that the dissolution of foraminifera shells did not produce a significant amount of fragments smaller than 63 m in size and thus the broecker clark size index is not a measure of the extent of fragmentation rather it is a measure of the extent of differential dissolution of foraminifera relative to coccoliths on the basis of these results we propose a new dissolution index which involves the ratio of dissolution susceptible foraminifera caco3 to total caco3

distribution of coccoliths in surface sediments of the south eastern south atlantic ocean ecology preservation and carbonate contribution abstract recent coccoliths from 52 surface sediment samples recovered from the south eastern south atlantic were examined qualitatively and quantitatively in order to assess the controlling mechanisms for their distribution patterns such as ecological and preservational factors and their role as carbonate producers total coccolith abundances range from 0 2 to 39 9 coccoliths 109 g 1 sediment four assemblages can be delineated by their coccolith content characterising the northern benguela the middle to southern benguela the walvis ridge and the deeper water distinctions are based on multivariate ordination techniques applied on the relative abundances of the most abundant taxa emiliania huxleyi calcidiscus leptoporus gephyrocapsa spp coccolithus pelagicus and subtropical to tropical species the coccolith distribution seems to be temperature and nutrient controlled co varying with the seaward extension of the upwelling filament zone in the benguela a preservation index cex based on the differential dissolution behaviour of the delicate e huxleyi and gephyrocapsa ericsonii versus the robust c leptoporus is applied in order to detect the position of the coccolith lysocline although some samples were recognised as dissolution affected the distribution of the coccoliths in the surface sediments reflects the different oceanographic surface water conditions mass estimations of the coccolith carbonate reveal coccoliths to be only minor contributors to the carbonate preserved in the surface sediments the mean computed coccolith carbonate content is 17 wt equivalent to a mean contribution of 23 to the bulk carbonate

planktic foraminiferal and sea surface temperature record during the last 1 myr across the subtropical front southwest pacific planktic foraminiferal faunas and modern analogue technique estimates of sea surface temperature sst for the last 1 million years myr are compared between core sites to the north odp 1125 178 faunas and south dsdp 594 374 faunas of the present location of the subtropical front stf east of new zealand faunas beneath cool subtropical water stw north of the stf are dominated by dextral neogloboquadrina pachyderma globorotalia inflata and globigerina bulloides whereas faunas to the south are strongly dominated by sinistral n pachyderma 80 95 in glacials with increased g bulloides 20 50 and dextral n pachyderma 15 50 in interglacials beneath subantarctic water or saw canonical correspondence analysis indicates that at both sites sst and related factors were the most important environmental influences on faunal composition greater climate related faunal fluctuations occur in the south significant faunal changes occur through time at both sites particularly towards the end of the mid pleistocene climate transition mis18 15 e g decline of globorotalia crassula in stw disappearance of globorotalia puncticulata in saw and during mis8 5 interglacial sst estimates in the north are similar to the present day throughout the last 1 myr to the south interglacial ssts are more variable with peaks 4 7 c cooler than present through much of the early and middle pleistocene but in mis11 mis5 5 and early mis1 peaks are estimated to have been 2 4 c warmer than present these high temperatures are attributed to southward spread of the stf across the submarine chatham rise along which the stf appears to have been dynamically positioned throughout most of the last 1 myr for much of the last 1 myr glacial sst estimates in the north were only 1 2 c cooler than the present interglacial except in mis16 mis8 mis6 and mis4 2 when estimates are 4 7 c cooler these cooler temperatures are attributed to jetting of saw through the mernoo saddle across the chatham rise and or waning of the stw current to the south glacial sst estimates were consistently 10 11 c cooler than present similar to temperatures and faunas currently found in the vicinity of the polar front one interpretation is that these cold temperatures reflect thermocline changes and increased circumpolar surface water spinning off the subantarctic front as an enhanced bounty gyre along the south side of the chatham rise for most of the last 1 myr the temperature gradient across the stf has been considerably greater than the present 4 c during glacial episodes the stf in this region did not migrate northwards but instead there was an intensification of the temperature gradient across it interglacials 4 11 c glacials 8 14 c

carbonate dissolution rates at the deep ocean floor 1 this paper reexamines experimental data on the seawater dissolution of caco3 bearing sediment beds to establish that the dependence of the calcite dissolution rate is linearly dependent on the calcite saturation state of the overlying water this linearity is inherent to the original data and is not the result of an error in the solubility product for calcite a comparison between these linear kinetics and the rate of solute transport across the benthic boundary layer further reveals that the overall rate of dissolution at ocean depths below the saturation horizon is controlled by boundary layer transfer a carbonate mass balance model for the sediment water interface which includes both kinetics and boundary layer effects predictively reproduces the currently observed caco3 depth distribution for two test areas in the oceans these findings allow important simplifications in modeling co2 neutralization in the oceans