variations in mode of formation and temperature of oceanic deep waters over the past 125 000 years marked changes in the deep water temperature of the different oceanic basins during the past 125 kyr are revealed by a detailed comparison of the oxygen isotopic composition ofbenthicforaminiferafrom sediment cores taken from the norwegian sea and the pacific atlantic and southern oceans the last interglacial deep water temperatures were similar to the modern ones at the 5e 5d transition around 115 kyr bp the deep water temperatures dropped below approximately 0 c in the pacific and southern indian oceans in the atlantic ocean the deep water temperature dropped in 2 successive steps at 115 and 75ky bp the global ocean deep water temperatures were in the 0 to 1 c range for the whole of the last ice age isotope stages 4 2

neritic and pelagic carbonate sedimentation in the marine environment ignorance is not bliss synthesis of available data allows us to define general patterns of late quaternary carbonate production and sedimentation in the global ocean during high stands of sea level the neritic and pelagic environments appear to sequester approximately similar amounts of carbonate whereas during low stands of sea level the decreased neritic zone produces and accumulates approximately an order of magnitude less carbonate assuming that global accumulation of deep sea carbonates remains more or less constant during glacially induced changes in sea level the ocean becomes depleted with respect to calcium carbonate during high stands and recharges during low stands before we can achieve a better understanding of the global carbonate system however we need a better understanding of key environments and processes a production and accumulation on continental shelves both as potential sinks accumulation and as sources export to the deep sea b a better measure of pelagic carbonate production and c late quaternary late pleistocene and holocene mass accumulation rates in the deep sea

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

mineralogy early marine diagenesis and the chemistry of shallow water carbonate sediments abstract shallow water carbonate sediments constitute the bulk of sedimentary carbonates in the geologic record and are widely used archives of earth s chemical and climatic history one of the main limitations in interpreting the geochemistry of ancient carbonate sediments is the potential for post depositional diagenetic alteration in this study we use paired measurements of calcium 44ca 40ca or 44ca and magnesium 26mg 24mg or 26mg isotope ratios in sedimentary carbonates and associated pore fluids as a tool to understand the mineralogical and diagenetic history of neogene shallow water carbonate sediments from the bahamas and southwest australia we find that the ca and mg isotopic composition of bulk carbonate sediments at these sites exhibits systematic stratigraphic variability that is related to both mineralogy and early marine diagenesis the observed variability in bulk sediment ca isotopes is best explained by changes in the extent and style of early marine diagenesis from one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the fluid fluid buffered to one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the precursor sediment sediment buffered our results indicate that this process together with variations in carbonate mineralogy aragonite calcite and dolomite plays a fundamental and underappreciated role in determining the regional and global stratigraphic expressions of geochemical tracers 13c 18o major minor and trace elements in shallow water carbonate sediments in the geologic record our results also provide evidence that a large shallow water carbonate sink that is enriched in 44ca can explain the mismatch between the 44 40ca value of rivers and deep sea carbonate sediments and call into question the hypothesis that the 44 40ca value of seawater depends on the mineralogy of primary carbonate precipitations e g aragonite seas and calcite seas finally our results for sedimentary dolomites suggest that paired measurements of ca and mg isotopes may provide a unique geochemical fingerprint of mass transfer during dolomitization to better understand the paleo environmental information preserved in these enigmatic but widespread carbonate minerals

influence of porewater advection on denitrification in carbonate sands evidence from repacked sediment column experiments abstract porewater flow enhances mineralization rates in organic poor permeable sands here a series of sediment column experiments were undertaken to assess the potential effect of advective porewater transport on denitrification in permeable carbonate sands collected from heron island great barrier reef experimental conditions flow path length advection rate and temperature were manipulated to represent conditions similar to near shore tropical environments hgcl2 poisoned controls were used to assess whether reactions were microbially mediated overall significant correlations were found between oxygen consumption and n2 production the n o2 slope of 0 114 implied that about 75 of all the nitrogen mineralized was denitrified a 4 fold increase in sediment column length from 10 to 40 cm resulted in an overall increase in oxygen consumption 1 6 fold tco2 production 1 8 fold and denitrification 1 9 fold oxic respiration increased quickly until advection reached 80 l m 2 h 1 and then plateaued at higher advection rates interestingly denitrification peaked up to 336 mol n2 m 2 h 1 at intermediate advection rates 30 80 l m 2 h 1 we speculate that intermediate advection rates enhance the development of microniches i e steep oxygen gradients within porous carbonate sands perhaps providing optimum conditions for denitrification the denitrification peak fell within the broad range of advection rates often on scales of 1 100 l m 2 h 1 typically found on continental shelves implying that carbonate sands may play a major but as yet unquantified role in oceanic nitrogen budgets

thorium 230 profiling in deep sea sediments high resolution records of flux and dissolution of carbonate in the equatorial atlantic during the last 24 000 years variations in carbonate flux and dissolution which occurred in the equatorial atlantic during the last 24 000 years have been estimated by a new approach that allows the point by point determination of paleofluxes to the seafloor an unprecedented time resolution can thus be obtained which allows sequencing of the relatively rapid events occurring during deglaciation the method is based on observations that the flux of unsupported 230th into deep sea sediments is nearly independent of the total mass flux and is close to the production rate thus excess 230th activity in sediments can be used as a reference against which fluxes of other sedimentary components can be estimated the study was conducted at two sites ceara rise western equatorial atlantic and sierra leone rise eastern equatorial atlantic in cores raised from three different depths at each site from measurements of 230th and caco3 changes in carbonate flux with time and depth were obtained a rapid increase in carbonate production starting at the onset of deglaciation was found in both areas this event may have important implications for the postglacial increase in atmospheric co2 by increasing the global carbonate carbon to organic carbon rain ratio and decreasing the alkalinity of surface waters and possibly the north atlantic deep water increased carbonate dissolution occurred in the two regions during deglaciation followed by a minimum during mid holocene and renewed intensification of dissolution in late holocene during the last 16 000 years carbonate dissolution was consistently more pronounced in the western than in the eastern basin reflecting the influence of antarctic bottom water in the west this trend was reversed during stage 2 possibly due to the accumulation of metabolic co2 below the level of the romanche fracture zone in the eastern basin

controls on carbonate mineral accumulation in bahamian basins and adjacent atlantic ocean sediments abstract carbonate mineralogical studies of surface bahamian periplatform ooze containing pelagic calcite as well as bank derived aragonite and magnesian calcite were coupled with studies of the carbonate chemistry of the waters overlying these sediments the presence of metastable aragonite and magnesian calcite in the periplatform ooze presents a unique opportunity to assess the relation between the extent of carbonate saturation in the water column and the disappearance of metastable carbonate minerals in an area of the north atlantic ocean where intermediate and deep waters are saturated with respect to calcite aragonite is present in the fine fraction of the surface sediment to a water depth of 4 800 m but decreases sharply below 4 000 m this is also the depth limit of the occurrence of pteropod tests and fragments in the coarse fraction of the sediment the aragonite compensation depth should be by extrapolation between 5 000 and 5 200 m the saturation depth with respect to aragonite was estimated to be located between 3 800 and 4 500 m this corresponds fairly well with the depth of a sharp decrease of the fine aragonite as well as the depth of pteropod disappearance magnesian calcite in the fine fraction of the sediment decreases irregularly with depth and disappears between 3 700 and 4 000 m the calculated saturation depth with respect to magnesian calcite 13 mole mgco3 is between 900 and 1 500 m at this depth a significant drop in the concentration of magnesian calcite occurs this decrease of magnesian calcite from 25 to 15 percent could be caused by both dissolution and the increasing distance of deeper waters from the banks however the higher values of specific alkalinity of the waters ranging between 750 and 2 000 m when compared with the alkalinity values of the sargasso sea at the same latitude are interpreted to be indicative that some dissolution of magnesian calcite occurs in the bahamian basins at these water dept s our results show depressed levels by 500 m or more of the aragonite saturation depth in the water column as well as of the depth of aragonite disappearance in the surface sediment when compared with open ocean studies in the northwest atlantic in addition our results indicate that fine magnesian calcite 12 to 13 mole mgco3 disappears 1 200 to 1 500 m above the extrapolated disappearance depth of aragonite this observation is consistent with results for experimental studies showing that aragonite is more stable in seawater than a magnesian calcite of 12 to 13 mole mgco3

the influence of pore water advection benthic photosynthesis and respiration on calcium carbonate dynamics in reef sands to investigate diel calcium carbonate caco3 dynamics in permeable coral reef sands we measured porewater profiles and fluxes of oxygen o2 nutrients ph calcium ca2 and alkalinity ta across the sediment water interface in sands of different permeability at heron reef australia background flushing rates were high most likely as a result of infaunal burrow irrigation but flux chamber stirring enhanced pore water exchange light and pore water advection fueled high rates of benthic primary production and calcification in sunlit surface sediments in the light benthic photosynthesis and calcification induced surface minima in ca2 and ta and peaks in ph and o2 oxygen penetration depth in coarse sands decreased from 1 2 cm during the day to 0 6 cm at night total oxygen uptake tou in dark chambers was three to fourteen times greater than diffusive uptake and showed a direct effect of pore water advection greater sediment oxygen consumption rates were observed in higher permeability sands in the dark ta release was not stimulated by increasing tou because of a damping effect of pore water advection on metabolic caco3 dissolution efficiency on a daily basis caco3 undergoes net dissolution in heron reef sands however pore water advection can reverse the caco3 budget and promote caco3 preservation under the most energetic conditions

in situ calcium carbonate dissolution in the pacific ocean over the past several years researchers have been working to synthesize the woce jgofs global co2 survey data to better understand carbon cycling processes in the oceans the pacific ocean data set has over 35 000 sample locations with at least two carbon parameters oxygen nutrients cfc tracers and hydrographic parameters in this paper we estimate the in situ caco3 dissolution rates in the pacific ocean water column calcium carbonate dissolution rates ranging from 0 01 1 1 mmol kg1 yr1 are observed in intermediate and deepwater beginning near the aragonite saturation horizon in the north pacific intermediate water between 400 and 800 m caco3 dissolution rates are more than 7 times faster than observed in middle and deep water depths average 0 051 mmol kg1 yr1 the total amount of caco3 that is dissolved within the pacific is determined by integrating excess alkalinity throughout the water column the total inventory of caco3 added by particle dissolution in the pacific ocean north of 40s is 157 pg c this amounts to an average dissolution rate of approximately 0 31 pg c yr1 this estimate is approximately 74 of the export production of caco3 estimated for the pacific ocean these estimates should be considered tomore be upper limits for in situ carbonate dissolution in the pacific ocean since a portion of the alkalinity increase results from inputs from sediments less

planktic foraminiferal sedimentation and the marine calcite budget 1 the vertical flux and sedimentation rate of planktic foraminiferal tests are quantified and a global planktic foraminiferal cac0 3 budget is presented test and calcite flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples modern planktic foraminiferal population dynamics are discussed as a prerequisite for the quantification of the calcite budget highlighting the importance of ecological autecological e g reproduction and biogeochemical conditions that determine the presence or absence of species to complete the open marine particulate caco 3 inventory the contribution of coccolithophores pteropods and calcareous dinophytes is discussed based on the studied regions the global planktic foraminiferal calcite flux rate at 100 m depth amounts to 1 3 3 2 gt yr 1 equivalent to 23 56 of the total open marine caco 3 flux the preservation of tests varies on a regional and temporal scale and is affected by local hydrography and dissolution during most of the year off peak periods many tests dissolve above 700 m water depth while settling through the water column with on average only 1 3 of the initially exported caco 3 reaching the deep seafloor pulsed flux events mass dumps of fast settling particles yield a major contribution of tests to the formation of deep sea sediments on average 25 of the initially produced planktic foraminiferal test cac0 3 settles on the seafloor the total planktic foraminiferal contribution of caco 3 to global surface sediments amounts to 0 36 0 88 gt yr 1 32 80 of the total deep marine calcite budget

neritic carbonate for six submerged coral reefs from northern australia implications for holocene global carbon dioxide abstract total contribution of six recently discovered submerged coral reefs in northern australia to holocene neritic caco3 and co2 is assessed to address a gap in global budgets caco3 production for the reef framework and inter reefal deposits is 0 26 0 28 mt holocene co2 production is 0 14 0 16 mt coral and coralline algae are the dominant sources of holocene caco3 although foraminifers and molluscs are the dominant constituents of inter reefal deposits the total amount of holocene neritic caco3 produced by the six submerged coral reefs is several orders of magnitude smaller than that calculated using accepted caco3 production values because of very low production a give up growth history and presumed significant dissolution and exports the contribution of submerged coral reefs to global holocene neritic caco3 is estimated to be 0 26 0 62 gt which yields 0 15 0 37 gt of co2 this amount of co2 is 0 02 0 05 of the 780 gt added to the atmosphere since 18 kyr bp contributions from australian submerged coral reefs are estimated to be 0 05 gt caco3 and 0 03 gt co2 for an emergent reef area of 47 9 103 km2 based on the growth history of the submerged coral reefs in the gulf of carpentaria maximum global holocene caco3 fluxes could have attained 0 3 gt yr 1 between 11 and 7 ka bp this additional caco3 would have culminated in a maximum caco3 production from all emergent and submerged coral reefs of 1 2 gt yr 1 and neritic caco3 production of 2 75 gt yr 1 the dilemma remains that the global area and caco3 mass of submerged coral reefs are currently unknown it is inevitable that many more submerged coral reefs will be found our findings imply that submerged coral reefs are a small but fundamental source of holocene neritic caco3 and co2

modern coral reefs of western atlantic new geological perspective contrary to popular belief of the late 1960s western atlantic holocene reefs have a long history and are not feeble novice nearshore veneers that barely survived postglacial temperatures rather the growth of these reefs kept pace with the rising seas of the holocene transgression and their development was for the most part controlled by offshore wave energy conditions and the relationship between changing sea levels and local shelf topography thus the outer shelves of the eastern caribbean in areas of high energy have relict reefs consisting predominantly of acropora palmata a robust shallow water coral the flooding of adjacent shelves during the postglacial transgression introduced stress conditions that terminated the growth of these reefs when about 7 000 r ago shelf water conditions improved scattered deeper water coral communities reestablished themselves on these stranded shelf edge reefs and fringing and bank barrier reefs began to flourish in shallow coastal areas at the same time the fragile and rapidly growing acropora cervicornis and other corals flourished at greater depths on the more protected shelves of the western caribbean and the gulf of mexico as a result late holocene buildups more than 30 m thick developed in those areas

coastal ocean co2 carbonic acid carbonate sediment system of the anthropocene 1 there is little doubt that human activities such as burning of fossil fuels and land use practices have changed and will continue to change the cycling of carbon in the global coastal ocean in the present study two biogeochemical box models were used to investigate the consequences of increasing atmospheric co2 and subsequent ocean acidification and increasing riverine transport of organic matter and nutrients arising from human activities on land on the global coastal ocean between the years 1700 and 2300 numerical simulations show that the net flux of co2 between coastal ocean surface water and the atmosphere is likely to change during this time from net evasion to net invasion owing to increasing atmospheric co2 increasing net ecosystem production arising from increasing nutrient loading to this region and decreasing net ecosystem calcification due to lower carbonate ion concentration and subsequent lower surface water saturation state with respect to carbonate minerals model calculations show that surface water saturation state with respect to calcite will decrease 73 by the year 2300 under a business as usual scenario which in concert with increasing temperature will cause overall biogenic calcification rate to decrease by 90 dissolution of carbonate minerals increased by 267 throughout the model simulation this increase was in part due to increased invasion of atmospheric co2 but mainly due to greater deposition and remineralization of land derived and in situ produced organic matter in the sediments producing co2 that caused pore water ph and carbonate saturation state to decrease this decrease in turn drove selective dissolution of metastable carbonate minerals as a consequence the relative carbonate composition of the sediments changed in favor of carbonate phases with lower solubility than that of an average 15 mol magnesian calcite phase model projected changes in surface water carbonate saturation state agree well with observations from the hawaiian ocean time series and the calculated air sea co2 exchange agrees well with a recent independent estimate of this flux derived from measurements from diverse coastal ecosystems scaled up to the global coastal ocean area

biogenic budgets of particle rain benthic remineralization and sediment accumulation in the equatorial pacific abstract budgets of organic c corg cac03 and opal have been constructed for the palisades ny pacific equatorial region at 140 w between 5 n and 5 s measurements of the rain and benthic remineralization rate of biogenic materials have been adjusted and normalized to account for sampling biases sea surface temperature serves as a master variable in normalizing sediment trap and benthic remineralization data to average conditions the rain and remineralization rates for corg are nearly equal 0 40 0 05 and 0 46 0 06 mmol m 2 d 1 respectively thus only a minor fraction of this constituent is buried rain and dissolution rates for biogenic opal are similarly balanced 0 3 0 06 and 0 36 0 01 mmol m 2 d 1 and consistent with the value for opal burial 0 0 0 004 the cac03 budget appears to have changed during the holocene the best estimates of modern cac03 dissolution 0 58 0 03 mmol m 2 d 1 and rain rate 0 61 0 06 are consistent with230th normalized carbonate accumulation rates for the late holocene 0 1 mmol m 2 d 1 however the balance between dissolution and rain is not consistent with early holocene carbonate accumulation 0 3 mmol m 2 d 1 and this imbalance suggests 1 a recent increase in the rate of cac03 dissolution on the sea floor or 2 a decrease in the rain rate of carbonate particles modeling230th profiles in sediments from this region define the last 3000 years as the duration of increased dissolution or decreased particle rain 231pa 230th ratios in sediments indicate that particle rain rates have remained constant or possibly increased slightly through the holocene two potential causes for increased dissolution were investigated a change in deep water carbonate saturation or a change in co g cac03 rain ratios a model describing carbonate dissolution as a function of the degree of undersaturation and the amount of organic carbon oxidation within sediments indicates that the recent increase in dissolution is more likely due to changes in bottom water chemical composition we propose that pacific ocean bottom water carbonate ion concentration has decreased by 10 15 m over the last 3000 years

neogene changes in southern ocean sedimentation based on mass accumulation rates at four continental margins 1 high resolution mass accumulation rates mar were determined from lithologic logs based on downhole log and continuous core data for six sites at four continental margins around the southern ocean total mar was calculated at ocean drilling program odp site 1095 on the margin of the antarctic peninsula and odp site 1165 on the margin of prydz bay antarctica carbonate and noncarbonate terrigenous mar were calculated for odp sites 1123 and 1124 east of new zealand and sites 1168 and 1172 west and southeast of tasmania shifts in carbonate mar are seen around tasmania and new zealand at 23 and 14 ma suggesting changes in deep water circulation and surface carbonate productivity at these times carbonate mar dropped at sites 1124 and 1168 at 23 ma and increased at 14 ma at sites 1123 1168 and 1172 the overall character of total mar at antarctic sites 1095 and 1165 is a continual and relatively constant decrease in total mar during the neogene with periods of stepwise decrease one such decrease is seen at 14 ma at site 1165 coincident with increased carbonate mar in new zealand and tasmania sites 1123 1124 1168 and 1172 and likely related to mid miocene expansion of the east antarctic ice sheet another step drop in total mar is seen at 9 ma at site 1165 possibly reflecting diversion of sediment to a newly formed prydz channel fan

shallow depth caco3 dissolution evidence from excess calcium in the south china sea and its export to the pacific ocean national basic research program of china 973 program 2009cb421201 2009cb421206 national science foundation of china nsfc 40821063 90711005 south china sea institute of oceanology the chinese academy of sciences

are seawater sr ca variations preserved in quaternary foraminifera abstract high precision measurements of sr ca in planktonic foraminifera for the last 150 ka reveal sr ca variations of up to 12 on glacial interglacial time scales although records showing the largest variations appear to be strongly influenced by selective dissolution other records show sr ca variations of 3 5 that do not covary with indicators of dissolution intensity and that are reproduced in sites of contrasting quaternary dissolution histories these systematic variations are characterized by high sr ca ratios during glacial maxima followed by steep decreases during deglaciation and gradual increases through interstadial periods closely following 18 o curves foraminiferal sr ca variations may reflect changes in the sr ca ratio of seawater or they may be due to kinetically or biologically induced changes in sr partitioning coupled numerical models of the sr and ca budgets of the ocean reveal that sea level changes together with large changes in river fluxes and carbonate accumulation rates can produce seawater sr ca variations that approximate both the shape and amplitude of foraminiferal sr ca variations however such extreme changes in river and carbonate fluxes conflict with existing data on carbonate accumulation rates and sr isotopic constraints on the magnitude of variations in the river flux smaller variations 1 3 in the sr ca ratio of seawater likely characterize quaternary glacial cycles changes in sr partitioning due to glacial interglacial changes in the carbonate ion concentration and other environmental factors likely produce additional variation in the sr ca record of planktonic foraminifera

diffusive cation fluxes in deep sea sediments and insight into the global geochemical cycles of calcium magnesium sodium and potassium the biogeochemical cycles of the ocean s major cations calcium magnesium sodium and potassium are linked to the ocean s alkalinity budget through terrestrial weathering and the subsequent formation and burial of calcium carbonate in the ocean chemical reactions within ocean sediments play a critical role in the biogeochemical cycles of the major cations as indicated by geochemical gradients both positive and negative in the concentrations of these cations within the pore fluid system i e fluid trapped between sediment particles here we review the biogeochemical cycles of calcium magnesium and sodium and provide new estimates of the diffusive fluxes of these cations within marine sediments to explore the importance of these sedimentary processes we quantify these fluxes by compiling a global database of pore fluids from the various ocean drilling programs deep sea drilling program dsdp ocean drilling program odp international ocean drilling program iodp comprising nearly 700 locations which allows a wider geographic coverage and therefore better integrated flux estimates than previous work has allowed the myriad of subseafloor chemical reactions that may influence the concentrations of the major cations in pore fluids include authigenic carbonate precipitation carbonate dissolution clay mineral formation and ion exchange as previous work has shown we confirm that these integrated fluxes are globally significant because the dsdp odp iodp cores begin sampling one meter below the sediment water interface additional studies of the processes within the top meter are needed to accurately calculate total cation fluxes across the sediment water interface delineating the various processes that control the major cation chemistry of seawater over geologic time scales remains critical for understanding the operation of the co2 silicate weathering thermostat on geologic timescales

the influence of organic matter diagenesis on caco3 dissolution at the deep sea floor abstract in situ benthic flux chamber measurements were performed at seafloor locations in the atlantic and pacific oceans where the bottomwaters were supersaturated approximately saturated and undersaturated with respect to calcite there was no evidence of significant dissolution at or above the saturation horizon below the saturation horizon however significant benthic fluxes of titration alkalinity and calcium out of the sediments were observed indicating appreciable dissolution where observed the rate of dissolution is consistent with a rate expression of reaction order 4 5 and a rate constant in the range of 0 05 to 0 5 per day a numerical simulation was constructed to represent organic matter and caco3 diagenesis at the seafloor at the supersaturated and near saturation sites the model over predicts the influence of metabolically produced co2 on the extent of caco3 dissolution it is possible that these results can be reconciled by a better understanding and parameterization of organic matter mineralization and porewater transport processes in surface sediments the primary factors to be considered include 1 the oxidation state of the carbon being oxidized 2 the vertical distribution of oxidation rates including the role of doc in sediment remineralization 3 the influence of nondiffusive transport of near surface porewaters and 4 the influence of episodic depositional events on organic and inorganic carbon cycling

underlying causes for long term global ocean δ13c fluctuations over the last 1 20 myr pleistocene stable carbon isotope 13c records from surface and deep dwelling foraminifera in all major ocean basins show two distinct long term carbon isotope fluctuations since 1 00 ma the first started around 1 00 ma and was characterised by a 0 35 decrease in 13c values until 0 90 ma followed by an increase of 0 60 lasting until 0 50 ma the subsequent fluctuation started with a 0 40 decrease between 0 50 and 0 25 ma followed by an increase of 0 30 between 0 25 and 0 10 ma here we evaluate existing evidence and various hypotheses for these global pleistocene 13c fluctuations and present an interpretation where the fluctuations most likely resulted from concomitant changes in the burial fluxes of organic and inorganic carbon due to ventilation changes and or changes in the production and export ratio our model indicates that to satisfy the long term stability of the pleistocene lysocline the ratio between the amounts of change in the organic and inorganic carbon burial fluxes would have to be close to a 1 1 ratio as deviations from this ratio would lead to sizable variations in the depth of the lysocline it is then apparent that the mid pleistocene climate transition which apart from the glacial cycles represents the most fundamental change in the pleistocene climate was likely not associated with a fundamental change in atmospheric pco2 while recognising that high frequency glacial interglacial cycles are associated with relatively large 100 ppmv changes in pco2 our model scenario with burial changes close to a 1 1 ratio produces a maximum long term variability of only 20 ppmv over the fluctuation between 1 00 and 0 50 ma

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

coastal ocean and carbonate systems in the high co2 world of the anthropocene the behavior of the ocean carbon cycle has been and will continue to be modified by the increase in atmospheric co2 due to fossil fuel combustion and land use emissions of this gas the consequences of a high co2 world and increasing riverine transport of organic matter and nutrients arising from human activities were investigated by means of two biogeochemical box models model numerical simulations ranging from the year 1700 to 2300 show that the global coastal ocean changes from a net source to a net sink of atmospheric co2 over time in the 18th and 19th centuries the direction of the co2 flux was from coastal surface waters to the atmosphere whereas at present or in the near future the net co2 flux is into coastal surface waters these results agree well with recent syntheses of measurements of air sea co2 exchange fluxes from various coastal ocean environments the model calculations also show that coastal ocean surface water carbonate saturation state would decrease 46 percent by the year 2100 and 73 percent by 2300 observational evidence from the pacific and atlantic oceans shows that the carbonate saturation state of surface ocean waters has already declined during recent decades for atolls and other semi enclosed carbonate systems the rate of decline depends strongly on the residence time of the water in the system based on the experimentally observed positive relationship between saturation state and calcification rate for many calcifying organisms biogenic production of caco3 may decrease by 42 percent by the year 2100 and by 85 to 90 percent by 2300 relative to its value of about 24 1012 moles c yr in the year 2000 if the predicted change in carbonate production were to occur along with rising temperatures it would make it difficult for coral reef and other carbonate systems to exist as we know them now into future centuries because high latitude cold water carbonates presently occur in waters closer to saturation with respect to carbonate minerals than the more strongly supersaturated waters of the lower latitudes it might be anticipated that the cool water carbonate systems might feel the effects of rising atmospheric co2 and temperature before those at lower latitudes in addition modeling results show that the carbonate saturation state of coastal sediment pore water will decrease in the future owing to a decreasing pore water ph and increasing co2 concentrations attributable to greater deposition and remineralization of land derived and in situ produced organic matter in sediments the lowered carbonate saturation state drives selective dissolution of metastable carbonate minerals while a metastable equilibrium is maintained between the pore water and the most soluble carbonate phase present in the sediments in the future the average composition of carbonate sediments and cements may change as the more soluble mg calcites and aragonite are preferentially dissolved and phases of lower solubility such as calcites with lower magnesium content increase in percentage abundance in the sediments

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

carbon cycling hysteresis in permeable carbonate sands over a diel cycle implications for ocean acidification dissolved inorganic carbon dissolved oxygen h and alkalinity fluxes from permeable carbonate sediments at heron island great barrier reef were measured over one diel cycle using benthic chambers designed to induce advective pore water exchange a complex hysteretic pattern between carbonate precipitation and dissolution in sands and the aragonite saturation state var of the overlying chamber water was observed throughout the incubations during the day precipitation followed a hysteretic pattern based on the incidence of photosynthetically active radiation with lower precipitation rates in the morning than in the afternoon the observed diel hysteresis seems to reflect a complex interaction between photosynthesis and respiration rather than var of the overlying water as the main driver of carbonate precipitation and dissolution within these permeable sediments changes in flux rates over a diel cycle demonstrate the importance of taking into account the shortterm variability of benthic metabolism when calculating net daily flux rates based on one diel cycle the sediments were a net daily source of alkalinity to the water column 5 13 to 8 84 mmol m22 d21 depending on advection rates and advection had a net stimulatory effect on carbonate dissolution the enhanced alkalinity release associated with benthic metabolism and pore water advection may partially buffer shallow coral reef ecosystems against ocean acidification on a local scale

significant contribution of authigenic carbonate to marine carbon burial carbon is removed from the earth s surface through the formation and burial of carbon bearing rocks and minerals an analysis of pore water profiles collected from marine sediments around the globe suggests that the precipitation of authigenic calcium carbonate accounts for around 10 of the carbonate that accumulates in marine sediments globally carbon is removed from the earth s surface through the formation and burial of carbon bearing rocks and minerals1 2 the formation of calcium carbonate and its burial in marine sediments accounts for around 80 of the total carbon removed from the earth s surface however the fraction of calcium carbonate that precipitates in the oceans versus that which precipitates authigenically in marine sediments is unclear here we compile measurements of the calcium concentration of pore fluids collected at 672 seafloor sites around the globe to calculate the global flux of calcium within marine sediments we use these data combined with alkalinity measurements of pore fluids to quantify authigenic calcium carbonate precipitation we estimate that the net calcium flux into marine sediments that can be ascribed to authigenic carbonate precipitation amounts to around 1 1012 mol yr 1 as such we estimate that authigenic carbonate precipitation accounts for at least 10 of global carbonate accumulation we show that much of the precipitation occurs along the eastern margins of ocean basins where organic matter delivery to the sea floor is likely to be high we suggest that authigenic calcium carbonate precipitation represents a non negligible component of the global carbon cycle

globally increased pelagic carbonate production during the mid brunhes dissolution interval and the co2 paradox of mis 11 the mid brunhes dissolution interval mbdi represents a period of global carbonate dissolution lasting several hundred thousand years centred around marine isotope stage mis 11 here we report the effects of dissolution in odp core 982 taken from 1134 m in the north atlantic paradoxically records of atmospheric co2 from antarctic ice cores reveal no long term trend over the last 400 kyr and suggest that co2 during mis 11 was no higher than during the present interglacial we suggest that a global increase in pelagic carbonate production during this period possibly related to the proliferation of the gephyrocapsa coccolithophore could have altered marine carbonate chemistry in such a way as to drive increased dissolution under the constraints of steady state an increase in the production of carbonate in surface waters would cause a drawdown of global carbonate saturation and increase dissolution at the seafloor in order to reconcile the record of atmospheric co2 variability we suggest that an increase in the flux of organic matter from the surface to deep ocean associated with either a net increase in primary production or the enhanced ballasting effect provided by an increased flux of caco3 could have countered the effect of increased calcification on co2

carbonate grain size distribution in hemipelagic sediments from a laser particle sizer laser grain sizer instruments provide the opportunity to study the grain size distribution of sediments across a wide size range in a short time automatic measurements can therefore be made on a routine basis for a great number of samples oceanic studies have proved the utility of these methods in characterizing both climatic changes and changes in sediment provenances in addition carbonate content is estimated either directly by caco 3 measurement by visual observations or by proxies such as sediment color reflectance nevertheless the grain size distribution of the carbonate fraction is still a matter of speculation and only optical observations can distinguish the nature of each carbonate fraction here we present the improvements on a method to study rapidly with a high resolution the grain size distribution of the carbonate fraction by use of a laser grain sizer we describe the basic methodology and apply it to an example from the pleistocene of the northern atlantic ocean

the solubility of fish produced high magnesium calcite in seawater 1 fish have been shown to produce high 10 to 48 mol magnesium calcite as part of the physiological mechanisms responsible for maintaining salt and water balance the importance of this source to the marine carbon cycle is only now being considered in this paper we report the first measurements of the solubility of this caco3 in seawater the resulting solubility pk sp 5 89 0 09 is approximately two times higher than aragonite and similar to the high magnesium calcite generated on the bahamas banks pk sp 5 90 this high solubility of fish produced caco3 is a result of the high magnesium content and not a product of micro environments created by microbial activity this material is soluble in near surface waters contributing to the input of carbonate to surface ocean waters and may at least partially explain the observed increase in total alkalinity above the aragonite saturation horizon

calcium isotopes in the marine environment and the oceanic calcium cycle abstract a systematic investigation of 44 ca 40 ca ratios in the oceanic ca cycle indicates that the average ca isotopic composition of input and output are quite different suggesting that the present ocean is not in a steady state our data show that sea water has uniform 44 ca 40 ca as expected from the long residence time of ca in the oceans it also exhibits the heaviest isotopic composition among all samples measured consistent with recent results by skulan et al 1997 and must be maintained at this value by strong biogenic isotope fractionation during the precipitation of caco 3 our measurements show that the riverine input is variable the most radiogenic river waters we have measured lowest 44 ca 40 ca are from ganges tributaries which also have high 87 sr 86 sr although there does not appear to be a systematic correlation between ca and sr isotopic compositions based on available data there is also significant isotopic variability among samples of caco 3 precipitated from the present ocean with coccolith oozes showing the most highly fractionated isotopic values relative to seawater among foraminifera ca isotopes exhibit species dependent fractionation effects but also appear to display systematic temperature dependent fractionation within inidividual species

from platform top to adjacent deep sea new source to sink insights into carbonate sediment production and transfer in the sw indian ocean glorieuses archipelago abstract over the past ten years a huge amount of source to sink studies have aimed to unravel the tectonic climatic and other processes that shape the landscape from mountains to the deep ocean interestingly these studies have been mainly dedicated to siliciclastic or mixed systems for which the connection between drainage basins continental shelves slope and basin environments are often well constrained here we present a study focusing on a source to sink study dedicated to a pure carbonate system located in the sw indian ocean glorieuses archipelago extensive field sampling and geophysical acquisition across the carbonate platform have allowed us to estimate the composition the lateral variability and volumes of neritic sands deposited on the platform top additional seismic and bathymetric surveys across the platform interior illustrate the presence of plurimetric sandy bodies deposited along the leeward platform edge corresponding to the export of carbonate sediments from the platform top toward the platform edge under the influence of dominant currents and wind driven processes high resolution seismic bathymetric data and sediment cores acquired along the leeward slope and basin adjacent to the carbonate platform highlight the presence of channel levee complexes and turbiditic lobes which have accumulated on the seafloor on top of a 250 m thick sedimentary basin at 2000 3400 m water depth our study points out that carbonate sands and aragonitic mud produced on the platform top during the holocene have been shed to the adjacent basin we also demonstrate that this routing system was active at least throughout the last three glacial interglacial cycles this study has important consequences for our understanding of carbonate sedimentation processes occurring in the vicinity of isolated carbonate platforms 1 it highlights the role of oceanographic conditions in the distribution of sediment on a platform top and its export along the platform edge and the adjacent basin 2 it contributes to quantify the productivity of a carbonate platform as well as its sediment storage capacity 3 a first estimate of a carbonate source to sink system is proposed demonstrating that 0 57 km3 of sediments have been produced during the holocene 0 3 km3 being presently stored on the platform and the remaining having been exported to the deep basin

cenozoic carbon cycle imbalances and a variable weathering feedback abstract the long term stability of earth s climate and the recovery of the ocean atmosphere system after carbon cycle perturbations are often attributed to a stabilizing negative feedback between silicate weathering and climate however evidence for the operation of this feedback over million year timescales and in response to tectonic and long term climatic change remains scarce for example the past 50 million years of the cenozoic era are characterized by long term cooling and declining atmospheric co2 p co 2 during this interval constant or decreasing carbon fluxes from the solid earth to the atmosphere suggest that stable or decreasing weathering fluxes are needed to balance the carbon cycle in contrast marine isotopic proxies of weathering i e 87sr 86sr 7 li and 187os 188os are interpreted to reflect increasing weathering fluxes here we evaluate the existence of a negative feedback by reconstructing the imbalance in the carbon cycle during the cenozoic using the surface inventories of carbon and alkalinity only a sustained 0 25 0 5 increase in silicate weathering is necessary to explain the long term decline in p co 2 over the cenozoic we propose that the long term decrease in p co 2 is due to an increase in the strength of the silicate weathering feedback i e the constant of proportionality between the silicate weathering flux and climate rather than an increase in the weathering flux this increase in the feedback strength which mirrors the marine isotope proxies occurs as transient 1 million year timescales remains invariant to match the long term inputs of carbon over the cenozoic this results in stable long term weathering fluxes even as p co 2 decreases we attribute increasing feedback strength to a change in the type and reactivity of rock in the weathering zone which collectively has increased the reactivity of the surface of the earth increasing feedback strength through the cenozoic reconciles mass balance in the carbon cycle with the marine isotopic proxies of weathering and may explain why there are periods when the earth system is more sensitive to carbon cycle perturbations

stress variability in the parnaiba basin brazil during cretaceous rifting the cretaceous section of the parnaiba basin designated as grajau basin represents an intracontinental half graben formed during the early cretaceous due to the separation between the south american and african continents during the final dispersal of western gondwana here through a synergetic approach between fluid inclusion planes fips outcropping geologic structures borehole breakouts and remote sensing data we elucidate in different scales the main structural features and their kinematic indicators normal faults strike mainly nne ssw and wnw ese while deformation bands and extension joints trend to nw se and ne sw and fips to ne sw and wnw ese in addition normal fault generated scarps border geomorphological units and constitute dense zones of deformation bands and fluidization microthermometric fip analyses suggest this fracturing event occurred at shallow basin levels at temperatures below 50 c furthermore joints bands and fips present mutually cross cutting relationships thus indicating contemporaneity the numerical inversions applied to striated faults non striated faults joints deformation bands and fips suggest the occurrence of an extensional event characterized by variable direction of extension 3 trending from nw se to wnw ese or ne se to nne ssw this event probably started in the albian during the final gondwana fragmentation stages the quasi perpendicular 3 trend could be caused by one or all of the following phenomena a stress ratio r values obtained 0 4 indicate the possibility of radial extension 2 3 perhaps in response to the deformation partitioning due to kinematic simple shearing constraints along the equatorial atlantic transform margin b along the wnw oriented release normal faults the local extension nne ssw switch positions in relation to the regional extension wnw ese by rotating 90 c influence of the pre existing structures on the regional stress field thus the spatial and temporal relationships between cretaceous fault activity stress field and the development of the geomorphological features in the grajau basin contribute to understanding of the brazilian equatorial margin geodynamics

accumulation of bank top sediment on the western slope of great bahama bank rapid progradation of a carbonate megabank high resolution seismic profiles and submersible observations along the leeward slope of western great bahama bank show large scale export of bank top sediment and rapid progradation of the slope during the holocene a wedge shaped sequence up to 90 m thick is present along most of the slope and consists of predominantly aragonite mud derived from the bank since flooding of the platform 6 8 ka total sediment volume of the slope sequence is 40 80 that of holocene sediment currently retained on the bank maximum rates of vertical accumulation and lateral progradation are 11 15 m ka and 80 110 m ka respectively 10 to 100 times greater than previously known for periplatform muds slope deposition of exported mud during sea level highs appears to have been a major mechanism for the westward progradation of great bahama bank throughout the quaternary this may provide a critical modern analogue for ancient progradational margins

effects of quaternary sea level cycles on strontium in seawater abstract the effects of quaternary sea level changes on the sr budget of the ocean are investigated using coupled numerical models of the seawater sr and ca budgets glacial interglacial sea level cycles influence the sr concentration of seawater directly through the periodic exposure and weathering of aragonite on continental shelves and indirectly by modulating the location and extent of carbonate deposition in the ocean as sea level recedes brief pulses of sr are added to the ocean from recrystallization of shelf aragonite this flux at its maximum is nearly ten times larger than the combined riverine and hydrothermal influx the large shelf recrystallization fluxes during glacial maxima produce rapid increases in the sr ca ratio of seawater despite the long residence time of sr in the ocean variations in the ratio of aragonitic vs calcitic sedimentation also influence on the sr content of seawater because the sr partitioning coefficient is higher in aragonite however this effect is minor compared to shelf aragonite recrystallization based on a variety of sensitivity tests the amplitude of sr ca variations ranges from 1 to 3 and is maximized by constant rates of total carbonate deposition extensive aragonite recrystallization and carbonate budgets which include dissolution of shelf carbonates such variation is sufficient to produce up to 1 5 c errors in paleotemperatures calculated from coral sr ca ratios since the last glacial maximum

the impact of calcareous nannofossils on the pelagic carbonate accumulation across the jurassic cretaceous boundary abstract calcareous nannofossils were important producers of pelagic carbonates in mesozoic oceans in order to better understand the origin of mesozoic pelagic carbonates we studied upper jurassic to lower cretaceous sediments in the central atlantic ocean dsdp sites 105 367 534a with respect to their content of calcareous nannofossils the interval under investigation is characterized by a significant increase in the deposition of carbonate rich sediments a trend that goes along with the rapid radiation of calcareous nannofossils the assemblage composition and the size variation of common taxa were analyzed and subsequently the contribution of this phytoplankton group to the pelagic carbonate accumulation was calculated results reveal two long term changes of the nannofossil assemblage composition 1 the early tithonian coccolith assemblages are of low diversity watznaueria spp cyclagelosphaera spp zeugrhabdotus spp whilst the mid to late tithonian assemblage is dominated by nannoliths conusphaera mexicana polycostella beckmannii nannoconus spp and large sized watznaueria 2 the early berriasian is characterized by a shift from the late tithonian nannolith rich assemblage to a highly diverse coccolith assemblage morphometric studies of the placolith genus watznaueria show for all three dsdp sites large sized forms of this genus in the mid and late tithonian followed by a decrease of up to 2 m for the mean size in the earliest berriasian at dsdp site 105 the studied nannolith taxa show an increase in size during the mid tithonian to berriasian interval the records of both nannofossil carbonate estimates and the measured bulk rock carbonate reveal two periods of increase in the nannofossil carbonate record of dsdp site 105 a first significant increase of the carbonate accumulation is observed in the mid and late tithonian probably caused by mass occurrences of strongly calcified taxa c mexicana p beckmannii nannoconus spp watznaueria cf manivitae this interval is here named nannofossil calcification event nce the second carbonate maximum in the late berriasian is related to a rise in absolute abundances of nannofossils this peak is amplified by an overall increase of the sedimentation rate the calculated accumulation rates of nannofossils nannofossil carbonate and bulk rock carbonate for the late berriasian are on the same scale as values from recent ocean surface sediments a comparison of nannofossil carbonate values with the bulk rock carbonate content shows that on average only 27 of the total carbonate can be explained by our nannofossil carbonate estimates this discrepancy is most likely caused by the high amount of unidentifiable micrite and fragments of calcareous nannofossils other factors contributing to the error are possible inaccuracies in the determination of absolute abundances and nannofossil volume calculations the nce occurs during a long term sea level fall dry climate and presumed low pco 2 levels a decline in abundance of strongly calcified nannofossils coincides with the opening of the pacific atlantic seaway via central america which may have had a substantial impact on the palaeoceanographic situation in the central atlantic ocean these changes are here considered to have at least partly caused the shifts in abundance size and assemblage composition of calcareous nannofossils observed across the jurassic cretaceous boundary interval

surface sediment carbonate mineralogy and water column chemistry nicaragua rise versus the bahamas abstract periplatform surface sediments were studied for carbonate mineralogy in conjunction with analyses of the water column for carbonate chemistry on the eastern northern nicaragua rise nnr in the caribbean sea the results show a strong correspondence between variations and disappearance with increasing water depth of metastable carbonate minerals fine aragonite and magnesian calcite and their respective saturation levels in the overlying waters similar correspondence between variations in sediment proportions of fine aragonite and magnesian calcite and their respective saturation levels has previously been established in the bahamas there are however significant differences between the two areas the sharp decrease in aragonite content and the measured aragonite saturation level occur at 4000 m in the bahamas compared to 1800 m on the eastern nnr in both areas magnesian calcite minima correspond to the in situ pco 2 maxima in the water column the magnesian calcite minimum however is at 950 m in the bahamas and 750 m on the eastern nnr magnesian calcite disappears in the bahamas at 3800 m and at 2000 m on the eastern nnr these results demonstrate the importance of the influence of overlying water chemistry on the preservation of metastable carbonate minerals in off bank periplatform sediments and they clearly demonstrate the difference in terms of carbonate preservation between the poorly ventilated waters of the caribbean sea and the well oxygenated waters of the adjacent atlantic ocean they also open the possibility of obtaining paleoceanographic information on the depth of the co 2 maximum o 2 minimum and its separation from the aragonite saturation depth in at least some areas

modeled estimates of global reef habitat and carbonate production since the last glacial maximum estimated changes in reef area and caco3 production since the last glacial maximum lgm are presented for the first time based on a model reefhab which uses measured environmental data to predict global distribution of reef habitat suitable reef habitat is defined by temperature salinity nutrients and the depth attenuated level of photosynthetically available radiation par caco3 production is calculated as a function of par when minimum par levels were chosen to restrict reef growth to 30 m depth and less modern reef area totaled 584 746 10 km global carbonate production which takes into account topographic relief as a control on carbonate accumulation was 1 00 gt yr 1 these values are close to the most widely accepted estimates of reef area and carbonate production and demonstrate that basic environmental data can be used to define reef habitat and calcification to simulate reef habitat changes since the lgm the model was run at 1 kyr intervals using appropriate sea level and temperature values these runs show that at the lgm reef area was restricted to 20 of that today and carbonate production to 27 due primarily to a reduction in available space at the lower sea level and secondarily to lower sea surface temperatures nonetheless these values suggest that reef growth prior to shelf flooding was more extensive than previously thought a crude estimate of reef released co2 to the atmosphere since the lgm is of the same order of magnitude as the atmospheric co2 change recorded in the vostok ice core which emphasizes the role of neritic carbonates within the global carbon cycle this model currently addresses only the major physical and chemical controls on reef carbonate production but it provides a template for estimating shallow tropical carbonate production both in the present and in the past as such the model highlights several long standing issues regarding reef carbonates particularly in terms of better defining the roles of light temperature aragonite saturation state and topography on reef calcification

high production and highstand shedding from deeply submerged carbonate banks northern nicaragua rise abstract because the shallow isolated carbonate banks on the northern nicaragua rise the nicaragua honduras and southern jamaica carbonate shelves and many other modern carbonate banks worldwide are covered by an average of 20 to 30 m of water and by a thin blanket of coarse carbonate sediments other carbonate sedimentologists have considered these banks good examples of incipiently drowned or even drowned carbonate banks however based on recent research on the northern nicaragua rise we can demonstrate that these banks currently are healthy producers of large volumes of periplatform sediments fine aragonite and magnesian calcite which are exported almost entirely to the deep surrounding slopes these sediments which were deposited during the past 9000 10 000 years form peripl tform wedges on the middle and upper slopes which are seen clearly on 3 5 khz seismic profiles radiocarbon ages of the wedge surface sediment range between 230 and 610 ybp and provide clear evidence for the contemporaneous production of sediments on the shallow bank and shelf and their instantaneous export to the upper slopes for the last 5000 years sedimentation rates ranged from 2000 mm ky off pedro bank to 1300 mm ky off jamaica these rates are somewhat lower than but of the same order of magnitude as sedimentation rates on the western leeward slopes of great bahama bank deposition of the metastable carbonate sediments discussed in this paper occurred as soon as sea level rose to flood the bank and shelf which flank walton basin following the last glacial lowstand they com rise a wedge shaped package of transgressive and highstand sediments on the upper and middle slopes of pedro bank and the southern jamaica shelf

understanding the causes and consequences of past marine carbon cycling variability through models abstract on geological time scales the production and degree of recycling of biogenic carbon in the marine realm and ultimately its removal to sediments exerts a dominant control on atmospheric co 2 and hence variability in climate this is a highly complex system involving a myriad of inter connected biological chemical and physical processes for this reason alone linking observations often highly abstracted in the form of proxies to the primary processes involved and ultimately to explanatory hypotheses for specific geological events and transitions is challenging the past few decades have seen a progressive improvement in theoretical and process based understanding of the various components that make up the marine carbon cycle and hand in hand with this the development of numerical model representations of the complete system models have also been designed and or adapted with paleoclimate questions in mind and applied to quantitatively explore the role of the marine carbon cycle in both perturbations and long term geologic evolutionary trends in global climate and possible feedbacks between them however we must ask whether paleoclimate models incorporate sufficiently appropriate representations of the dynamics and sensitivities of the marine carbon cycle and indeed whether in the geological context we really know what these dynamics are here we provide a comprehensive overview of how marine carbon cycling and the biological carbon pump is treated in available paleoclimate models with the aim of critically evaluating their ability to help interpret past marine carbon cycle and climate dynamics to this end we first provide an overview of commonly used paleoclimate models and some of their associated paleo applications drawing from a wide range of global carbon cycle box models and earth system models of intermediate complexity emics secondly we review and evaluate the three dominant processes involved in the cycling of organic and inorganic carbon in the marine system and how they are represented in models namely biological productivity at the ocean surface remineralisation dissolution of particulate carbon within the water column and the benthic pelagic coupling at the seafloor we generate and employ illustrative examples using the model genie to show how different parameterisations of water column and sediment processes can lead to significantly different model projections our compilation reveals the prevalence of static parameterisations of marine carbon cycling among existing paleoclimate models which are commonly empirically derived from present day observations although such approaches tend to represent carbon transfer in the modern ocean well they are potentially compromised in their ability to reflect the true degree of freedom and strength of feedbacks with respect to past climate events particularly those characterised by environmental boundary conditions that differ fundamentally from today finally we discuss the importance of using models of different complexities and how questions of model uncertainty may start to be addressed

constraining the marine strontium budget with natural strontium isotope fractionations 87sr 86sr δ88 86sr of carbonates hydrothermal solutions and river waters we present strontium sr isotope ratios that unlike traditional 87sr 86sr data are not normalized to a fixed 88sr 86sr ratio of 8 375209 defined as 88 86sr 0 relative to nist srm 987 instead we correct for isotope fractionation during mass spectrometry with a 87sr 84sr double spike this technique yields two independent ratios for 87sr 86sr and 88sr 86sr that are reported as 87sr 86sr and 88 86sr respectively the difference between the traditional radiogenic 87sr 86sr normalized to 88sr 86sr 8 375209 and the new 87sr 86sr values reflect natural mass dependent isotope fractionation in order to constrain glacial interglacial changes in the marine sr budget we compare the isotope composition of modern seawater 87sr 86sr 88 86sr seawater and modern marine biogenic carbonates 87sr 86sr 88 86sr carbonates with the corresponding values of river waters 87sr 86sr 88 86sr river and hydrothermal solutions 87sr 86sr 88 86sr hydend in a triple isotope plot the measured 87sr 86sr 88 86sr river values of selected rivers that together account for not vert similar18 of the global sr discharge yield a sr flux weighted mean of 0 7114 8 0 315 8 the average 87sr 86sr 88 86sr hydend values for hydrothermal solutions from the atlantic ocean are 0 7045 5 0 27 3 in contrast the 87sr 86sr 88 86sr carbonates values representing the marine sr output are 0 70926 2 0 21 2 we estimate the modern sr isotope composition of the sources at 0 7106 8 0 310 8 the difference between the estimated 87sr 86sr 88 86sr input and 87sr 86sr 88 86sr output values reflects isotope disequilibrium with respect to sr inputs and outputs in contrast to the modern ocean isotope equilibrium between inputs and outputs during the last glacial maximum 10 30 ka before present can be explained by invoking three times higher sr inputs from a uniquely glacial source weathering of shelf carbonates exposed at low sea levels our data are also consistent with the weathering peak hypothesis that invokes enhanced sr inputs resulting from weathering of post glacial exposure of abundant fine grained material

a simple model for the caco3 saturation state of the ocean the strangelove the neritan and the cretan ocean 1 a simple model of the caco3 saturation state of the ocean is presented it can be solved analytically and is intended to identify the fundamental controls on ocean carbonate ion concentration it should also attract researchers unfamiliar with complex biogeochemical models despite its limitations the model calculated caco3 saturation state of today s ocean agrees well with observations in general the model reveals three distinctly different modes of operation the strangelove ocean of high supersaturation which is dominated by inorganic caco3 precipitation 2 the neritan ocean of indefinite saturation dominated by biogenic shallow water caco3 precipitation and 3 the cretan ocean of low saturation dominated by biogenic pelagic caco3 precipitation in the latter mode the deep ocean co32 is remarkably stable provided that the biogenic production of caco3 exceeds the riverine flux of ca2 and co32 this explains the overall constancy of the saturation state of the ocean documented over the last 100 ma the model is then used to address diverse questions one important result is that the recovery of the oceanic carbonate chemistry from fossil fuel neutralization in the future will be accelerated due to expected reduced biogenic calcification

late quaternary caco3 production and preservation in the southern ocean implications for oceanic and atmospheric carbon cycling recent geochemical models invoke ocean alkalinity changes particularly in the surface southern ocean to explain glacial age pco2 reduction in such models alkalinity increases in glacial periods are driven by reductions in north atlantic deep water nadw supply which lead to increases in deep water nutrients and dissolution of carbonate sediments and to increased alkalinity of circumpolar deep water upwelling in the surface southern ocean we use cores from the southeast indian ridge and from the deep cape basin in the south atlantic to show that carbonate dissolution was enhanced during glacial stages in areas now bathed by circumpolar deep water this suggests that deep southern ocean carbonate ion concentrations were lower in glacial stages than in interglacials rather than higher as suggested by the polar alkalinity model broecker and peng 1989 our observations show that changes in southern ocean caco3 preservation are coherent with changes in the relative flux of nadw suggesting that southern ocean carbonate chemistry is closely linked to changes in deepwater circulation the pattern of enhanced dissolution in glacials is consistent with a reduction in the supply of nutrient depleted water nadw to the southern ocean and with an increase of nutrients in deep water masses carbonate mass accumulation rates on the southeast indian ridge 3200 3800 m and in relatively shallow cores 3000 m from the kerguelen plateau and the south pacific were significantly reduced during glacial stages by about 50 the reduced carbonate mass accumulation rates and enhanced dissolution during glacials may be partly due to decreases in caco3 corg flux ratios acting as another mechanism which would raise the alkalinity of southern ocean surface waters the polar alkalinity model assumes that the ratio of organic carbon to carbonate production on surface alkalinity is constant even if overall productivity in the southern ocean were held constant a decrease in the caco3 corg ratio would result in increased alkalinity and reduced pco2 in southern ocean surface waters during glacials this ecologically driven surface alkalinity change may enhance deepwater mediated changes in alkalinity and amplify rapid changes in pco2

holocene sediments of wistari reef towards a global quantification of coral reef related neritic sedimentation in the holocene wistari reef within the southern great barrier reef is a shallow coral reef platform featuring a very clearly defined leeward accretionary wedge of carbonate sediments the total global area of shallowly submerged coral reef has been quantified as 255 000 km 2 the question then becomes what additional area of sediment of significant thickness is associated with the measured shallow reef areas t at wistari reef the leeward sedimentary wedge has an area and a thickness that are roughly equal to the holocene sediments that have accumulated on the platform several important observations can be made from these data firstly the area of significant neritic carbonate sedimentation 1 m ka associated with coral reefs is near 500000 km 2 secondly the production rate of neritic carbonates at wistari reef is almost 50 less than the accumulation rate needed to obtain the volume of holocene reef sediments observed this implies that both production and accumulation neritic carbonate must have been more than a factor of two higher in the early to mid holocene c 2001 elsevier science b v all rights reserved

effects of early sea floor processes on the taphonomy of temperate shelf skeletal carbonate deposits abstract cool water shelf carbonates differ from tropical carbonates in their sources modes and rates of deposition geochemistry and diagenesis inorganic precipitation marine cementation and sediment accumulation rates are absent or slow in cool waters so that temperate carbonates remain longer at or near the sea bed early sea floor processes occurring between biogenic calcification and ultimate deposition thus take on an important role and there is the potential for considerable taphonomic loss of skeletal information into the fossilised record of cool water carbonate deposits the physical breakdown processes of dissociation breakage and abrasion are mediated mainly by hydraulic regime and are always destructive impact damage reduces the size of grains removes structure and therefore information and ultimately may transform skeletal material into anonymous particles abrasion is highly selective amongst and within taxa their skeletal form and structure strongly influencing resistance to mechanical breakdown dissolution and precipitation are the end members of a two way chemical equilibrium operating in sea water in cool waters inorganic precipitation is rare there is conflicting opinion about the importance of diagenetic dissolution of carbonate skeletons on the temperate sea floor but test maceration and early loss of aragonite in particular are reported dissolution may relate to undersaturated acidic pore waters generated locally by a combination of microbial metabolisation of organic matter strong bioturbation and oxidation of solid phase sulphides immediately beneath the sea floor in otherwise very slowly accumulating skeletal deposits laboratory experiments demonstrate that surface to volume ratio and skeletal mineralogy are both important in determining skeletal resistance to dissolution biological processes on the sea floor include encrustation and bioerosion encrustation a constructive process may be periodic or seasonal and can be reversed it produces both information and material bioerosion in contrast is destructive and permanent in temperate areas bioerosion may destroy even very large shells during their long residence at the sea floor on the order of hundreds to thousands of years overall processes on the temperate sea floor may combine to destroy more carbonate than they produce and the preservation potential of temperate shelf carbonate into the rock record may be significantly affected where preservation does occur in such a destructive regime the effects of early sea floor processes will be key determinants of the deposit resulting in a taphofacies characteristic of temperate shelf carbonate sediments

glacial deep ocean sequestration of co2 driven by the eastern equatorial pacific biologic pump abstract the potential influence of low latitude ocean primary productivity on glacial atmospheric carbon dioxide levels has proven challenging to deduce using mass accumulation rates mars of biogenic particulates in deep sea sediment cores benthic foraminiferal b ca serves as a proxy for past seawater calcite saturation state and thereby provides a fresh perspective on this outstanding paleoceanographic problem here we employ cibicidoides wuellerstorfi b ca in the panama basin region of the eastern equatorial pacific eep to investigate the nature of deep tropical pacific carbon storage over the past 50 ka bp we present evidence for persistently lower deep panama basin calcite saturation state reflecting an increase in total carbon dioxide storage during the last ice age relative to the holocene these results reflect the modification of inflowing deep waters by overlying export productivity and support the concept of an invigorated glacial eep soft tissue pump possibly driven by oceanic nutrient iron and silica redistribution benthic cibicidoides spp carbon 13 is consistent with this conclusion by exhibiting substantially lighter values during glacial time reflecting the accumulation of metabolic carbon dioxide in the deep tropical pacific counterintuitively downcore application of the globorotalia menardii calcite fragmentation index mfi reveals enhanced glacial sedimentary calcite preservation in the panama basin together these results point towards a systematic decoupling of bottom water chemistry from biogenic burial fluxes the crux of the aforementioned traditional paleoproductivity problem

rapid passage of a small scale mantle heterogeneity through the melting regions of kilauea and mauna loa volcanoes recent kilauea and mauna loa lavas provide a snapshot of the size shape and distribution of compositional heterogeneities within the hawaiian mantle plume here we present a study of the pb sr and nd isotope ratios of two suites of young prehistoric lavas from these volcanoes 1 kilauea summit lavas erupted from ad 900 to 1400 and 2 14 c dated mauna loa flows erupted from 2580 140 yr before present relative to ad 1950 these lavas display systematic isotopic fluctuations and the kilauea lavas span the pb isotopic divide that was previously thought to exist between these two volcanoes for a brief period from ad 250 to 1400 the 206 pb 204 pb and 87 sr 86 sr isotope ratios and end values of kilauea and mauna loa lavas departed from values typical for each volcano based on historical and other young prehistoric lavas moved towards an intermediate composition and subsequently returned to typical values this is the only known period in the eruptive history of these volcanoes when such a simultaneous convergence of pb sr and nd isotope ratios has occurred the common isotopic composition of lavas erupted from both kilauea and mauna loa during this transient magmatic event was probably caused by the rapid passage of a small scale compositional heterogeneity through the melting regions of both volcanoes this heterogeneity is thought to have been either a single body 35 km long based on the distance between the summits of these volcanoes or the plume matrix itself which would be expected to be present beneath both volcanoes the time scale of this event centuries is much shorter than previously noted for variations in the isotopic composition of hawaiian lavas due to the upwelling of heterogeneities within the plume thousands to tens of thousands of years calculations based on the timing of the isotopic convergence suggest a maximum thickness for the melting region and thus the heterogeneity of 5 10 km the small size of the heterogeneity indicates that melt can be extracted from small regions within the hawaiian plume with minimal subsequent chemical modification beyond the effects of crystal

the impact of electrogenic sulfide oxidation on elemental cycling and solute fluxes in coastal sediment abstract filamentous sulfide oxidizing cable bacteria are capable of linking the oxidation of free sulfide in deep anoxic layers of marine sediments to the reduction of oxygen or nitrate in surface sediments by conducting electrons over centimeter scale distances previous studies have shown that this newly discovered microbial process referred to as electrogenic sulfide oxidation e sox may alter elemental cycling in sediments but the nature and rates of the resulting biogeochemical transformations and their influence on benthic pelagic coupling remain largely unknown here we quantify changes in sediment geochemistry and solute fluxes at the sediment water interface as e sox develops and declines over time in laboratory incubations of organic rich sediments from a seasonally hypoxic coastal basin marine lake grevelingen the netherlands our results show that e sox enhanced sediment o2 consumption and acidified subsurface sediment resulting in the dissolution of calcium carbonate and iron sulfide minerals in deeper sediment horizons and the associated accumulation of dissolved iron manganese and calcium in porewater remobilized fe diffusing upward was reoxidized at the sediment water interface producing an amorphous fe oxide crust while dissolved fe diffusing downward was reprecipitated in the form of fes as it encountered the free sulfide horizon the development of e sox enhanced the diffusive release of dissolved mn at the sediment water interface capped the phosphate efflux generated a buildup of organic matter in surface sediments and strongly stimulated the release of alkalinity from the sediment about 75 of this alkalinity production was associated with net caco3 dissolution while the remaining 25 was attributed to a pumping mechanism that transfers alkalinity from anodic h2s oxidation an alkalinity sink in deeper sediments to cathodic o2 reduction an alkalinity source near the sediment water interface the resulting sediment alkalinity efflux buffers the release of dissolved inorganic carbon at the sediment water interface and may therefore counteract the influence of benthic respiration on coastal ocean ph overall our results demonstrate that e sox development strongly affects the biogeochemical cycles of c p ca fe mn and s in coastal sediments