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Henry Elderfield - One of the best experts on this subject based on the ideXlab platform.

  • the effect of ocean alkalinity and carbon transfer on deep sea Carbonate Ion concentratIon during the past five glacial cycles
    Earth and Planetary Science Letters, 2017
    Co-Authors: Rosalind E M Rickaby, Aleksey Sadekov, Henry Elderfield
    Abstract:

    Abstract Glacial–interglacial deep Indo-Pacific Carbonate Ion concentratIon ([ CO 3 2 − ]) changes were mainly driven by two mechanisms that operated on different timescales: 1) a long-term increase during glaciatIon caused by a Carbonate depositIon reductIon on shelves (i.e., the coral reef hypothesis), and 2) transient Carbonate compensatIon responses to deep ocean carbon storage changes. To investigate these mechanisms, we have used benthic foraminiferal B/Ca to reconstruct deep-water [ CO 3 2 − ] in cores from the deep Indian and Equatorial Pacific Oceans during the past five glacial cycles. Based on our reconstructIons, we suggest that the shelf-to-basin shift of Carbonate depositIon raised deep-water [ CO 3 2 − ], on average, by 7.3 ± 0.5 (SE) μmol/kg during glaciatIons. Oceanic carbon reorganisatIons during major climatic transitIons caused deep-water [ CO 3 2 − ] deviatIons away from the long-term trend, and Carbonate compensatIon processes subsequently acted to restore the ocean Carbonate system to new steady state conditIons. Deep-water [ CO 3 2 − ] showed similar patterns to sediment Carbonate content (%CaCO3) records on glacial–interglacial timescales, suggesting that past seafloor %CaCO3 variatIons were dominated by deep-water Carbonate preservatIon changes at our studied sites.

  • mg ca compositIon of benthic foraminifera miliolacea as a new tool of paleoceanography
    Paleoceanography, 2014
    Co-Authors: Aleksey Sadekov, Flora Bush, Joanna Kerr, Raja S Ganeshram, Henry Elderfield
    Abstract:

    The Mg/Ca compositIons of benthic foraminifera from the superfamily Miliolacea have been studied to explore the use of these high-Mg foraminifera as a proxy for deep ocean conditIons. Taxonomic analyses, relative abundance, and depth distributIons of different Miliolacea species were carried out on a collectIon of core top samples, covering a depth range of 131 m to 2530 m, along the Australian coast of the Timor Sea. Pyrgo sp., composed of Pyrgo sarsi and Pyrgo murrhina, was found to be the most suitable for proxy studies. Mg/Ca values of this group of foraminifera show a strong correlatIon with bottom water temperatures and Carbonate Ion saturatIon described by the linear relatIonship: Mg/Ca = 2.53(±0.22) × BWT + 0.129(±0.023) × Δ[CO32−] + 4.63(±0.53), within the −1°C to 8°C temperature range. Absolute Mg/Ca values of Pyrgo sp. calcite and their temperature sensitivity are similar to those observed for inorganic calcite, suggesting that Mg compositIon of Pyrgo sp. calcite is mainly controlled by inorganic processes. The Mg/Ca compositIon of Pyrgo sp. calcite provides a new tool for reconstructing both water temperature and Carbonate Ion saturatIon when combined with other proxies for one of these parameters. A down core record from the Eastern Equatorial Pacific has been generated to illustrate how Mg/Ca values can be used for paleoclimate studies. This down core record shows large changes in Pacific bottom waters [CO32−] across glacial-interglacial transitIon, implying an increase in [CO32−] during the glacial period.

  • mg ca in the benthic foraminifera cibicidoides wuellerstorfi and cibicidoides mundulus temperature versus Carbonate Ion saturatIon
    Earth and Planetary Science Letters, 2008
    Co-Authors: Jimin Yu, Henry Elderfield
    Abstract:

    Magnesium/calcium (Mg/Ca) ratios in two widely used benthic foraminiferal species, Cibicidoides wuellerstorfi and Cibicidoides mundulus (Cibicidoides kullenbergi), picked from global ocean core-tops and from six cores in the North Atlantic Ocean have been measured to investigate Mg/Ca variability, cleaning effect, and influences from bottom water temperature (BWT) and deep water Carbonate Ion saturatIon (Δ[CO32−]). Replicate measurements of the two species reveal Mg/Ca variability of 0.07 ± 0.07 mmol/mol. Compared with Mg/Ca in samples cleaned by oxidative cleaning, Mg/Ca ratios are significantly lowered, by 0.10 ± 0.09 mmol/mol, in samples cleaned by reductive cleaning, likely due to preferential leaching during the reductive cleaning step. The cleaning influence is large relative to glacial–interglacial Mg/Ca changes (0.05–0.31 mmol/mol by this study). RegressIon of core-top data from a wide range of locatIons show that C. wuellerstorfi Mg/Ca is strongly affected by deep water Δ[CO32−] with a sensitivity of ~ 0.009 mmol/mol per µmol/kg. When BWT is included in regressIons, the correlatIon is slightly more significant with a weak BWT sensitivity on Mg/Ca of between 0.03 ± 0.01 and 0.07 ± 0.02 mmol/mol per °C. Because Δ[CO32−] and BWT co-vary for most core-top samples, an alternate method of separating the two effects was made by comparing glacial to interglacial changes in Mg/Ca from a depth transect of North Atlantic cores where the BWT and Carbonate Ion histories since the last glacial period have been well constrained. Results from this transect suggest that the BWT effect is < 0.03 mmol/mol per °C, weaker than inferred from the core-top study. Therefore, core-top and down core data suggest that C. wuellerstorfi Mg/Ca is insensitive to BWT changes. The weak BWT effect, when compared with natural variability, complicates the use of Mg/Ca in this species to reconstruct past BWT. Taking all measured samples from various environments into account, C. mundulus Mg/Ca ratios show no correlatIon with BWT or deep water Δ[CO32−].

  • foraminiferal calcificatIon response to glacial interglacial changes in atmospheric co2
    Science, 2002
    Co-Authors: Stephen Barker, Henry Elderfield
    Abstract:

    A record of foraminiferal shell weight across glacial-interglacial TerminatIon I shows a response related to seawater Carbonate Ion concentratIon and allows reconstructIon of a record of carbon dioxide in surface seawater that matches the atmospheric record. The results support suggestIons that higher atmospheric carbon dioxide directly affects marine calcificatIon, an effect that may be of global importance to past and future changes in atmospheric CO2. The process provides negative feedback to the influence of marine calcificatIon on atmospheric carbon dioxide and is of practical importance to the applicatIon of paleoceanographic proxies.

Aleksey Sadekov - One of the best experts on this subject based on the ideXlab platform.

  • the effect of ocean alkalinity and carbon transfer on deep sea Carbonate Ion concentratIon during the past five glacial cycles
    Earth and Planetary Science Letters, 2017
    Co-Authors: Rosalind E M Rickaby, Aleksey Sadekov, Henry Elderfield
    Abstract:

    Abstract Glacial–interglacial deep Indo-Pacific Carbonate Ion concentratIon ([ CO 3 2 − ]) changes were mainly driven by two mechanisms that operated on different timescales: 1) a long-term increase during glaciatIon caused by a Carbonate depositIon reductIon on shelves (i.e., the coral reef hypothesis), and 2) transient Carbonate compensatIon responses to deep ocean carbon storage changes. To investigate these mechanisms, we have used benthic foraminiferal B/Ca to reconstruct deep-water [ CO 3 2 − ] in cores from the deep Indian and Equatorial Pacific Oceans during the past five glacial cycles. Based on our reconstructIons, we suggest that the shelf-to-basin shift of Carbonate depositIon raised deep-water [ CO 3 2 − ], on average, by 7.3 ± 0.5 (SE) μmol/kg during glaciatIons. Oceanic carbon reorganisatIons during major climatic transitIons caused deep-water [ CO 3 2 − ] deviatIons away from the long-term trend, and Carbonate compensatIon processes subsequently acted to restore the ocean Carbonate system to new steady state conditIons. Deep-water [ CO 3 2 − ] showed similar patterns to sediment Carbonate content (%CaCO3) records on glacial–interglacial timescales, suggesting that past seafloor %CaCO3 variatIons were dominated by deep-water Carbonate preservatIon changes at our studied sites.

  • mg ca compositIon of benthic foraminifera miliolacea as a new tool of paleoceanography
    Paleoceanography, 2014
    Co-Authors: Aleksey Sadekov, Flora Bush, Joanna Kerr, Raja S Ganeshram, Henry Elderfield
    Abstract:

    The Mg/Ca compositIons of benthic foraminifera from the superfamily Miliolacea have been studied to explore the use of these high-Mg foraminifera as a proxy for deep ocean conditIons. Taxonomic analyses, relative abundance, and depth distributIons of different Miliolacea species were carried out on a collectIon of core top samples, covering a depth range of 131 m to 2530 m, along the Australian coast of the Timor Sea. Pyrgo sp., composed of Pyrgo sarsi and Pyrgo murrhina, was found to be the most suitable for proxy studies. Mg/Ca values of this group of foraminifera show a strong correlatIon with bottom water temperatures and Carbonate Ion saturatIon described by the linear relatIonship: Mg/Ca = 2.53(±0.22) × BWT + 0.129(±0.023) × Δ[CO32−] + 4.63(±0.53), within the −1°C to 8°C temperature range. Absolute Mg/Ca values of Pyrgo sp. calcite and their temperature sensitivity are similar to those observed for inorganic calcite, suggesting that Mg compositIon of Pyrgo sp. calcite is mainly controlled by inorganic processes. The Mg/Ca compositIon of Pyrgo sp. calcite provides a new tool for reconstructing both water temperature and Carbonate Ion saturatIon when combined with other proxies for one of these parameters. A down core record from the Eastern Equatorial Pacific has been generated to illustrate how Mg/Ca values can be used for paleoclimate studies. This down core record shows large changes in Pacific bottom waters [CO32−] across glacial-interglacial transitIon, implying an increase in [CO32−] during the glacial period.

Kevin Huang - One of the best experts on this subject based on the ideXlab platform.

  • A superior mixed electron and Carbonate-Ion conducting metal-Carbonate composite membrane for advanced flue-gas carbon capture
    Journal of Membrane Science, 2016
    Co-Authors: Jie Fang, Jingjing Tong, Kevin Huang
    Abstract:

    Developing cost-effective, energy-efficient and CO2-selective advanced carbon capture technologies for carbon intensive flue gas is of vital importance to the reductIon of carbon pollutIon and mitigatIon of global climate change. In the present work, we report that an electrochemistry-based mixed electron and Carbonate-Ion conducting metal-Carbonate composite membrane with porous metal matrix fabricated by a chemical dealloying method exhibits superior CO2/O2 flux density and stability over a 900-h testing period. The results also demonstrate that the presence of H2 in the sweeping gas can significantly enhance the CO2 flux density as a result of increased gradient of chemical potential of oxygen and produce a pure stream of CO2 and H2O for easy downstream conversIon. The fundamental mechanisms leading to the superior performance are also discussed.

  • silver molten Carbonate composite as a new high flux membrane for electrochemical separatIon of co2 from flue gas
    Journal of Membrane Science, 2012
    Co-Authors: Xue Li, Nansheng Xu, Maxwell A Franks, Hailei Zhao, Kevin Huang
    Abstract:

    Abstract One of the major concerns of consuming fossil fuels to produce useful form of energy is the emissIon of CO 2 , a greenhouse gas that can cause climate change and ultimately threaten the survival of humanity. Controlling CO 2 -emissIon is an urgent but only practical solutIon to stabilize CO 2 concentratIon in the atmosphere. In this paper, we report our effort to capture CO 2 from a simulated flue gas by utilizing a dual-phase mixed Carbonate-Ion and electron conducting membrane, namely molten Carbonate and silver. The obtained CO 2 and O 2 flux densities are the highest among the published metal-molten Carbonate systems and relatively stable over 80-h period. The measured CO 2 and O 2 flux densities not only exhibit similar activatIon energy but also have the ratio of 2:1, favorably confirming the surface electrochemical reactIon of CO 2  + 1/2O 2  + 2e′ = CO 3 2− . These results demonstrate the Ag–MC dual-phase composite as a promising high-flux membrane for high-temperature electrochemical CO 2 separatIon from flue gas with high selectivity.

  • effective Ionic conductivity of a novel intermediate temperature mixed oxide Ion and Carbonate Ion conductor
    Journal of The Electrochemical Society, 2011
    Co-Authors: Guoliang Xiao, Kevin Huang
    Abstract:

    The discovery of new fast Ionic conductors has been long pursued by solid state chemists due to the important roles they play in modern solid state Ionic devices. The Sr- and Mg-doped LaGaO3 LSGM perovskite oxide-Ion conductor discovered in the mid1990s is a good example illustrating the fruitIon of years’ of continual efforts in this area. The oxide-Ion conductivity of LSGM at 800°C is as high as that of Y2O3-doped ZrO2 at 1000°C and is stable over a broad range of partial pressures of oxygen. As an electrolyte of the solid oxide fuel cell SOFC, these attributes connote higher chemical-to-electrical conversIon efficiency or less performance loss at a given temperature and/or reduced operating temperature for a given performance. The latter is of practical importance because lowering the operating temperature of an SOFC could drastically improve the performance stability and reduce the system cost, the two foremost obstacles presently impeding the commercializatIon of the SOFC technology. The common features of existing good oxide-Ion conductors such as ZrO2-, CeO2-, and LaGaO3-based oxides can be characterized by oxygen vacancies available in the lattice and cubic structure of high symmetry. 1-3

Richard E. Zeebe - One of the best experts on this subject based on the ideXlab platform.

  • on the molecular diffusIon coefficients of dissolved co2 hco3 and co32 and their dependence on isotopic mass
    Geochimica et Cosmochimica Acta, 2011
    Co-Authors: Richard E. Zeebe
    Abstract:

    Abstract The molecular diffusIon coefficients of dissolved carbon dioxide ( CO 2 ) , biCarbonate Ion ( HCO 3 - ) , and Carbonate Ion ( CO 3 2 - ) are fundamental physico-chemical constants and are of practical significance in various disciplines including geochemistry, biology, and medicine. Yet, very little experimental data is available, for instance, on the biCarbonate and Carbonate Ion diffusIon coefficient. Furthermore, it appears that no informatIon was hitherto available on the mass-dependence of the diffusIon coefficients of the Ionic Carbonate species in water. Here I use molecular dynamics simulatIons to study the diffusIon of the dissolved Carbonate species in water, including their dependence on temperature and isotopic mass. Based on the simulatIons, I provide equatIons to calculate the diffusIon coefficients of dissolved CO 2 , HCO 3 - , and CO 3 2 - over the temperature range from 0° to 100 °C. The results indicate a mass-dependence of CO 2 diffusIon that is consistent with the observed 12 CO 2 / 13 CO 2 diffusIon ratio at 25 °C. No significant isotope fractIonatIon appears to be associated with the diffusIon of the naturally occurring isotopologues of HCO 3 - and CO 3 2 - at 25 °C.

  • reversed deep sea Carbonate Ion basin gradient during paleocene eocene thermal maximum
    Paleoceanography, 2007
    Co-Authors: Richard E. Zeebe, James C Zachos
    Abstract:

    [1] The Paleocene-Eocene thermal maximum (PETM, ∼55 Ma ago) was marked by widespread CaCO3 dissolutIon in deep-sea sediments, a process that has been attributed to massive release of carbon into the ocean-atmosphere system. The pattern of Carbonate dissolutIon is key to reconstructing changes in deep sea Carbonate chemistry and, ultimately, the rate, magnitude, and locatIon of carbon input. Here we show that during the PETM, the deep-sea undersaturatIon was not homogeneous among the different ocean basins. ApplicatIon of a sediment model to a suite of data records from different sites and ocean basins shows that a globally uniform decrease in deep-sea Carbonate Ion concentratIon ([CO32−]) is inconsistent with the data. Rather, we demonstrate that deep-sea [CO32−] increased from the Atlantic through the Southern Ocean into the Pacific. Our results show that the PETM deep-sea [CO32−] basin gradient during dissolutIon was reversed relative to the modern.

  • history of Carbonate Ion concentratIon over the last 100 millIon years
    Geochimica et Cosmochimica Acta, 2004
    Co-Authors: Toby Tyrrell, Richard E. Zeebe
    Abstract:

    Abstract Instead of having been more or less constant, as once assumed, it is now apparent that the major Ion chemistry of the oceans has varied substantially over time. For instance, independent lines of evidence suggest that calcium concentratIon ([Ca2+]) has approximately halved and magnesium concentratIon ([Mg2+]) approximately doubled over the last 100 millIon years. On the other hand, the calcite compensatIon depth, and hence the CaCO3 saturatIon, has varied little over the last 100 My as documented in deep sea sediments. We combine these pieces of evidence to develop a proxy for seawater Carbonate Ion concentratIon ([CO32−]) over this period of time. From the calcite saturatIon state (which is proportIonal to the product of [Ca2+] times [CO32−], but also affected by [Mg2+]), we can calculate seawater [CO32−]. Our results show that [CO32−] has nearly quadrupled since the Cretaceous. Furthermore, by combining our [CO32−] proxy with other Carbonate system proxies, we provide calculatIons of the entire seawater Carbonate system and atmospheric CO2. Based on this, reconstructed atmospheric CO2 is relatively low in the Miocene but high in the Eocene. Finally, we make a strong case that seawater pH has increased over the last 100 My.

  • a simple model for the caco3 saturatIon state of the ocean the strangelove the neritan and the cretan ocean
    Geochemistry Geophysics Geosystems, 2003
    Co-Authors: Richard E. Zeebe, Peter Westbroek
    Abstract:

    [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.

Wallace S Broecker - One of the best experts on this subject based on the ideXlab platform.

  • is the magnitude of the Carbonate Ion decrease in the abyssal ocean over the last 8 kyr consistent with the 20 ppm rise in atmospheric co2 content
    Paleoceanography, 2007
    Co-Authors: Wallace S Broecker, Elizabeth Clark
    Abstract:

    [1] Changes in the extent of shell fragmentatIon, the wall thicknesses of foraminifera shells, and the bulk CaCO3 content of deep Pacific sediments demonstrate that the extent of dissolutIon has steadily increased during the past 8 kyr. On the basis of measurements on sediment core top material from a range of water depths on the Ontong-Java Plateau, these dissolutIon proxies have been calibrated, allowing the extent of the decrease in Carbonate Ion concentratIon to be quantified. The results suggest that the decrease was larger than that of 6 μmol/km expected to accompany the 20 μatm rise in atmospheric CO2 content that occurred during this time interval. However, the inconsistency between the magnitude of the change based on the decrease in shell weight on one hand and that based on the increase in fragmentatIon on the other hand is problematic. If indeed the drop in Carbonate Ion concentratIon has been larger than expected, then 8 kyr ago either a change in the pattern of thermohaline circulatIon or in the strength of the biological pump must have kicked in and become ever stronger as the millennia passed. If thermohaline circulatIon is the villain, then a possible explanatIon is that the strength of deepwater formatIon in the northern Atlantic has weakened relative to that in the Southern Ocean.

  • evidence for a reductIon in the Carbonate Ion content of the deep sea during the course of the holocene
    Paleoceanography, 1999
    Co-Authors: Wallace S Broecker, Elizabeth Clark, Daniel C Mccorkle, Tsunghung Peng, Irena Hajdas, Georges Bonani
    Abstract:

    The paleo Carbonate Ion proxy proposed by Broecker et al. [1999] is applied in a search for trends in the Holocene acidity of waters in the transitIon zone between North Atlantic Deep Water and Antarctic Bottom Water (AABW). A clear signal emerges that the Carbonate Ion content of waters in this zone declined during the past 8000 years. In order to determine whether this decline represents a strengthening of the northward penetrating tongue of low CO3= content AABW or a global reductIon of CO3=Ion, measurements were made on a core from the Ontong Java Plateau in the western equatorial Pacific. Evidence for a similar decline in CO3=Ion over the course of the Holocene was obtained lending support of the latter explanatIon. Such a drop is consistent with the recent finding by Indermuhle et al. [1999] that the CO2 content of the atmosphere (as recorded in the Taylor Dome Antarctica ice core) rose by 20–25 ppm during the past 8000 years.

  • evidence for a higher ph in the glacial ocean from boron isotopes in foraminifera
    Nature, 1995
    Co-Authors: Abhijit Sanyal, N G Hemming, Gilbert N Hanson, Wallace S Broecker
    Abstract:

    RECORDS of past changes in the pH of the oceans should provide insights into how the Carbonate chemistry of the oceans has changed over time. The latter is related to changes in the atmospheric CO2 content, such as that which occurred during the last glacial-interglacial transitIon1. Previous studies2,3 have shown that the fractIonatIon of boron isotopes between sea water and precipitated Carbonate minerals is pH-dependent. This finding has been used to reconstruct the evolutIon of ocean pH over the past 20 millIon years by analyses of boron isotopes in the Carbonate shells of foraminifera4. Here we use the same approach to estimate changes in ocean pH between the last glacial and the Holocene period. We estimate that the deep Atlantic and Pacific oceans had a pH 0.3±0.1 units higher during the last glaciatIon. The accompanying change in Carbonate Ion concentratIon is sufficient to account for the decrease in atmospheric pco2 during the glacial period1. These results are consistent with the hypothesis5 that the low CO2 content of the glacial atmosphere was caused by an increased ratio of organic carbon to Carbonate in the 'rain' to the sea floor, which led to an increase in Carbonate Ion concentratIon (and thus in pH) of deep water without a corresponding increase in the lysocline depth.