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Helmuth Thomas - One of the best experts on this subject based on the ideXlab platform.

  • The impact of intertidal areas on the Carbonate System of the southern North Sea
    Biogeosciences, 2020
    Co-Authors: Fabian Schwichtenberg, Helmuth Thomas, Johannes Pätsch, Michael Ernst Böttcher, Vera Winde, Kay-christian Emeis
    Abstract:

    Abstract. The coastal ocean is strongly affected by ocean acidification because of its shallow water depths, low volume, and the closeness to terrestrial dynamics. Earlier observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) in the southern part of the North Sea, a northwest European shelf sea, revealed lower acidification effects than expected. It has been assumed that anaerobic degradation and subsequent TA release in the adjacent back-barrier tidal areas (Wadden Sea) in summertime is responsible for this phenomenon. In this study the exchange rates of TA and DIC between the Wadden Sea tidal basins and the North Sea and the consequences for the Carbonate System in the German Bight are estimated using a 3D ecoSystem model. The aim of this study is to differentiate the various sources contributing to observed high summer TA in the southern North Sea. Measured TA and DIC in the Wadden Sea are considered as model boundary conditions. This procedure acknowledges the dynamic behaviour of the Wadden Sea as an area of effective production and decomposition of organic material. According to the modelling results, 39 Gmol TA yr −1 were exported from the Wadden Sea into the North Sea, which is less than a previous estimate but within a comparable range. The interannual variabilities in TA and DIC, mainly driven by hydrodynamic conditions, were examined for the years 2001–2009. Dynamics in the Carbonate System are found to be related to specific weather conditions. The results suggest that the Wadden Sea is an important driver for the Carbonate System in the southern North Sea. On average 41 % of TA inventory changes in the German Bight were caused by riverine input, 37 % by net transport from adjacent North Sea sectors, 16 % by Wadden Sea export, and 6 % were caused by internal net production of TA. The dominant role of river input for the TA inventory disappears when focusing on TA concentration changes due to the corresponding freshwater fluxes diluting the marine TA concentrations. The ratio of exported TA versus DIC reflects the dominant underlying biogeochemical processes in the Wadden Sea. Whereas aerobic degradation of organic matter played a key role in the North Frisian Wadden Sea during all seasons of the year, anaerobic degradation of organic matter dominated in the East Frisian Wadden Sea. Despite the scarcity of high-resolution field data, it is shown that anaerobic degradation in the Wadden Sea is one of the main contributors of elevated summer TA values in the southern North Sea.

  • The recent state and variability of the Carbonate System of the Canadian Arctic Archipelago and adjacent basins in the context of ocean acidification
    Biogeosciences, 2020
    Co-Authors: Alexis Beaupré-laperrière, Alfonso Mucci, Helmuth Thomas
    Abstract:

    Abstract. Ocean acidification driven by the uptake of anthropogenic CO2 by the surface oceans constitutes a potential threat to the health of marine ecoSystems around the globe. The Arctic Ocean is particularly vulnerable to acidification and thus is an ideal region to study the progression and effects of acidification before they become globally widespread. The appearance of undersaturated surface waters with respect to the Carbonate mineral aragonite ( ΩA ), an important threshold beyond which the calcification and growth of some marine organisms might be hindered, has recently been documented in the Canada Basin and adjacent Canadian Arctic Archipelago (CAA), a dynamic region with an inherently strong variability in biogeochemical processes. Nonetheless, few of these observations were made in the last 5 years and the spatial coverage in the latter region is poor. We use a dataset of Carbonate System parameters measured in the CAA and its adjacent basins (Canada Basin and Baffin Bay) from 2003 to 2016 to describe the recent state of these parameters across the Canadian Arctic and investigate the amplitude and sources of the System's variability over more than a decade. Our findings reveal that, in the summers of 2014 to 2016, the ocean surface across our study area served as a net CO2 sink and was partly undersaturated with respect to aragonite in the Canada Basin and the Queen Maud Gulf, the latter region exhibiting undersaturation over its entire water column at some locations. We estimate, using measurements made across several years, that approximately a third of the interannual variability in surface dissolved inorganic carbon (DIC) concentrations in the CAA results from fluctuations in biological activity. In consideration of the System's variability resulting from these fluctuations, we derive times of emergence of the anthropogenic ocean acidification signal for Carbonate System parameters in the study area.

  • The impact of intertidal areas on the Carbonate System of the southern North Sea
    2020
    Co-Authors: Fabian Schwichtenberg, Helmuth Thomas, Johannes Pätsch, Michael Ernst Böttcher, Vera Winde, Kay-christian Emeis
    Abstract:

    Abstract. The coastal ocean is strongly affected by ocean acidification because it is shallow and has a low volume. Earlier observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) in the southern part of the North Sea and the German Bight, a Northwest-European shelf sea, have revealed lower acidification effects than expected. It has been assumed that anaerobic degradation and subsequent TA release in the adjacent tidal areas (Wadden Sea) in summer time is responsible for this phenomenon. In this study the exchange rates of TA and DIC between the Wadden Sea and the North Sea and the consequences for the Carbonate System in the German Bight are estimated using a 3-D ecoSystem model. Observed TA and DIC sources in the Wadden Sea were considered as boundary conditions. This procedure is based on the dynamic behaviour of the Wadden Sea as an area of effective production and decomposition of organic material. In addition, modelled tidal water mass exchange was used to transport material between the open North Sea and the Wadden Sea. In the model, 39 Gmol TA yr−1 were exported from the Wadden Sea into the North Sea, which is lower than a previous estimate, but within a comparable range. Furthermore, the interannual variabilities of TA and DIC concentrations, which were mainly driven by hydrodynamic conditions, were examined for the years 2001–2009. Variability in the Carbonate System of the German Bight is related to weather in that the occurrence of weak meteorological blocking situations leads to enhanced accumulation of TA there. The results suggest that the Wadden Sea is an important driver of the Carbonate System variability in the southern North Sea. According to the model results, on average 63 % of all TA mass changes in the German Bight were caused by net transport, 25 % by Wadden Sea export, 9 % were caused by the internal production of TA and 3 % caused by effective TA river loads (i.e. river load including freshwater dilution). The ratio of exported TA and DIC reflects the dominant underlying biogeochemical processes in the different Wadden Sea areas. Aerobic degradation of organic matter plays a key role in the North Frisian Wadden Sea during all seasons of the year. In the East Frisian Wadden Sea anaerobic degradation of organic matter dominated.

  • The internal consistency of the North Sea Carbonate System
    Journal of Marine Systems, 2016
    Co-Authors: Lesley A. Salt, Helmuth Thomas, Yann Bozec, Alberto V. Borges, Hein J W De Baar
    Abstract:

    In 2002 (February) and 2005 (August) the full suite of Carbonate System parameters (Total Alkalinity (AT), Dissolved Inorganic Carbon (DIC), pH, and partial pressure of CO2 (pCO2) were measured on two re-occupations of the entire North Sea basin, with three parameters (AT, DIC, pCO2) measured on four additional re-occupations, covering all four seasons, allowing an assessment of the internal consistency of the Carbonate System. For most of the year there is a similar level of internal consistency, with AT being calculated to within ± 6 μmol kg- 1 using DIC and pH, DIC to ± 6 μmol kg- 1 using AT and pH, pH to ± 0.008 using AT and pCO2, and pCO2 to ± 8 μatm using DIC and pH, with the dissociation constants of Millero et al. (2006). In spring, however, we observe a significant decline in the ability to accurately calculate the Carbonate System. Lower consistency is observed with an increasing fraction of Baltic Sea water, caused by the high contribution of organic alkalinity in this water mass, not accounted for in the Carbonate System calculations. Attempts to improve the internal consistency by accounting for the unconventional salinity-borate relationships in freshwater and the Baltic Sea, and through application of the new North Atlantic salinity-boron relationship (Lee et al., 2010), resulted in no significant difference in the internal consistency.

  • The internal consistency of the North Sea Carbonate System
    Journal of Marine Systems, 2016
    Co-Authors: Lesley Salt, Helmuth Thomas, Yann Bozec, Alberto Borges, Hein J W De Baar
    Abstract:

    International audienceIn 2002 (February) and 2005 (August) the full suite of Carbonate System parameters (Total Alkalinity (AT), Dissolved Inorganic Carbon (DIC), pH, and partial pressure of CO2 (pCO2) were measured on two re-occupations of the entire North Sea basin, with three parameters (AT, DIC, pCO2) measured on four additional re-occupations, covering all four seasons, allowing an assessment of the internal consistency of the Carbonate System. For most of the year there is a similar level of internal consistency, with AT being calculated to within ± 6 μmol kg- 1 using DIC and pH, DIC to ± 6 μmol kg- 1 using AT and pH, pH to ± 0.008 using AT and pCO2, and pCO2 to ± 8 μatm using DIC and pH, with the dissociation constants of Millero et al. (2006). In spring, however, we observe a significant decline in the ability to accurately calculate the Carbonate System. Lower consistency is observed with an increasing fraction of Baltic Sea water, caused by the high contribution of organic alkalinity in this water mass, not accounted for in the Carbonate System calculations. Attempts to improve the internal consistency by accounting for the unconventional salinity-borate relationships in freshwater and the Baltic Sea, and through application of the new North Atlantic salinity-boron relationship (Lee et al., 2010), resulted in no significant difference in the internal consistency

Gavin L. Foster - One of the best experts on this subject based on the ideXlab platform.

  • Evaluating the utility of B/Ca ratios in planktic foraminifera as a proxy for the Carbonate System: A case study of Globigerinoides ruber
    Geochemistry Geophysics Geosystems, 2015
    Co-Authors: Michael J. Henehan, James W. B. Rae, Gavin L. Foster, Katy C. Prentice, Jonathan Erez, Helen C. Bostock, Brittney J. Marshall, Paul A. Wilson
    Abstract:

    B/Ca ratios in foraminifera have attracted considerable scientific attention as a proxy for past ocean Carbonate System. However, the Carbonate System controls on B/Ca ratios are not straightforward, with ?[ inline image] ([ inline image]in situ – [ inline image]at saturation) correlating best with B/Ca ratios in benthic foraminifera, rather than pH, inline image, or inline image (as a simple model of boron speciation in seawater and incorporation into CaCO3 would predict). Furthermore, culture experiments have shown that in planktic foraminifera properties such as salinity and [B]sw can have profound effects on B/Ca ratios beyond those predicted by simple partition coefficients. Here, we investigate the controls on B/Ca ratios in G. ruber via a combination of culture experiments and core-top measurements, and add to a growing body of evidence that suggests B/Ca ratios in symbiont-bearing foraminiferal Carbonate are not a straightforward proxy for past seawater Carbonate System conditions. We find that while B/Ca ratios in culture experiments covary with pH, in open ocean sediments this relationship is not seen. In fact, our B/Ca data correlate best with [ inline image] (a previously undocumented association) and in most regions, salinity. These findings might suggest a precipitation rate or crystallographic control on boron incorporation into foraminiferal calcite. Regardless, our results underscore the need for caution when attempting to interpret B/Ca records in terms of the ocean Carbonate System, at the very least in the case of mixed-layer planktic foraminifera.

  • Boron isotopes and B/Ca in benthic foraminifera: proxies for the deep ocean Carbonate System
    Earth and Planetary Science Letters, 2011
    Co-Authors: James W. B. Rae, Gavin L. Foster, Daniela N Schmidt, Tim Elliott
    Abstract:

    Abstract Accurate records of the state of the ocean Carbonate System are critical for understanding past changes in pCO 2 , ocean acidification and climate. The chemical principles underlying the proxy of oceanic pH provided by the boron isotope ratio of foraminiferal Carbonate are relatively well understood, but the proxy's reliability has been questioned. We present 76 new Multi-Collector Inductively-Coupled Plasma Mass Spectrometry (MC-ICPMS) δ 11 B measurements on a range of benthic foraminifera from 23 late-Holocene samples from the Atlantic that reaffirm the utility of the δ 11 B-pH proxy. Our boron isotope measurements on ~ 10 benthic foraminifera tests typically yield a precision of ~ ± 0.25‰ at 2 s.d. (equivalent to ~ ± 0.03 pH units). δ 11 B values of epifaunal species are within analytical uncertainty of those predicted from a simple model assuming sole incorporation of B(OH) 4 − from seawater and no vital effects, using the independently determined fractionation factor of 1.0272 between 11 B/ 10 B of aqueous boron species. Infaunal foraminifera are consistent with this model, but record the combined effects of lower pore-water δ 11 B and pH. No influence of partial dissolution or shell size on δ 11 B is observed. We have also measured the B/Ca ratios of the same samples. For individual Cibicidoides species, B/Ca shows a good correlation with Δ[CO 3 2− ], but the B/Ca of different co-occurring species morphotypes varies considerably. These effects are not seen in δ 11 B, which may therefore provide a more robust proxy of the ocean Carbonate System. Whilst in theory δ 11 B and B/Ca can be combined to provide a quantitative reconstruction of alkalinity and dissolved inorganic Carbonate (DIC), in practice this is precluded by propagated uncertainties. δ 11 B data give significant constraints on foraminifera calcification mechanisms, and seem most simply explained by incorporation of B(OH) 4 − into a HCO 3 − pool, which is then completely incorporated in foraminiferal CaCO 3 . Our demonstration of the predictable variation of δ 11 B with pH, across a wide range of species and locations, provides confidence in the application of MC-ICPMS measurements of foraminiferal δ 11 B to reconstruct past changes in the ocean Carbonate System.

  • A core top assessment of proxies for the ocean Carbonate System in surface‐dwelling foraminifers
    Paleoceanography, 2007
    Co-Authors: Gavin L. Foster, Daniela N Schmidt, Tim Elliott, T. R. Bailey, Paul Nicholas Pearson, Brian A. Haley, Christopher D. Coath
    Abstract:

    We have assessed the reliability of several foraminifer-hosted proxies of the ocean Carbonate System (δ 11B, B/Ca, and U/Ca) using Holocene samples from the Atlantic and Pacific oceans. We examined chemical variability over a range of test sizes for two surface-dwelling foraminifers (Globigerinoides sacculifer and Globigerinoides ruber). Measurements of δ 11B in G. ruber show no significant relationship with test size in either Atlantic or Pacific sites and appear to provide a robust proxy of surface seawater pH. Likewise there is no significant variability in the δ 11B of our Atlantic core top G. sacculifer, but we find that δ 11B increases with increasing test size for G. sacculifer in the Pacific. These Systematic differences in δ 11B are inferred to be a consequence of isotopically light gametogenic calcite in G. sacculifer and its preferential preservation during postdepositional dissolution. The trace element ratio proxies of ocean Carbonate equilibria, U/Ca and B/Ca, show Systematic increases in both G. ruber and G. sacculifer with increasing test size, possibly as a result of changing growth rates. This behavior complicates their use in paleoceanographic reconstructions. In keeping with several previous studies we find that Mg/Ca ratios increase with increasing size fraction in our well-preserved Atlantic G. sacculifer but not in G. ruber. In contrast to previous interpretations we suggest that these observations reflect a proportionally larger influence of compositionally distinct gametogenic calcite in small individuals compared to larger ones. As with δ 11B this influences G. sacculifer but not G. ruber, which has negligible gametogenic calcite.

  • A core top assessment of proxies for the ocean Carbonate System in surface-dwelling foraminifers
    Paleoceanography, 2007
    Co-Authors: Gavin L. Foster, Daniela N Schmidt, Tim Elliott, Trevor Bailey, Paul Pearson, Brian Haley, Christopher D. Coath
    Abstract:

    We have assessed the reliability of several foraminifer-hosted proxies of the ocean Carbonate System (d11B,\ud B/Ca, and U/Ca) using Holocene samples from the Atlantic and Pacific oceans. We examined chemical\ud variability over a range of test sizes for two surface-dwelling foraminifers (Globigerinoides sacculifer and\ud Globigerinoides ruber). Measurements of d11B in G. ruber show no significant relationship with test size in\ud either Atlantic or Pacific sites and appear to provide a robust proxy of surface seawater pH. Likewise there is no\ud significant variability in the d11B of our Atlantic core top G. sacculifer, but we find that d11B increases with\ud increasing test size for G. sacculifer in the Pacific. These Systematic differences in d11B are inferred to be a\ud consequence of isotopically light gametogenic calcite in G. sacculifer and its preferential preservation during\ud postdepositional dissolution. The trace element ratio proxies of ocean Carbonate equilibria, U/Ca and B/Ca,\ud show Systematic increases in both G. ruber and G. sacculifer with increasing test size, possibly as a result of\ud changing growth rates. This behavior complicates their use in paleoceanographic reconstructions. In keeping\ud with several previous studies we find that Mg/Ca ratios increase with increasing size fraction in our wellpreserved\ud Atlantic G. sacculifer but not in G. ruber. In contrast to previous interpretations we suggest that these\ud observations reflect a proportionally larger influence of compositionally distinct gametogenic calcite in small\ud individuals compared to larger ones. As with d11B this influences G. sacculifer but not G. ruber, which has\ud negligible gametogenic calcite

Christopher D. Coath - One of the best experts on this subject based on the ideXlab platform.

  • A core top assessment of proxies for the ocean Carbonate System in surface‐dwelling foraminifers
    Paleoceanography, 2007
    Co-Authors: Gavin L. Foster, Daniela N Schmidt, Tim Elliott, T. R. Bailey, Paul Nicholas Pearson, Brian A. Haley, Christopher D. Coath
    Abstract:

    We have assessed the reliability of several foraminifer-hosted proxies of the ocean Carbonate System (δ 11B, B/Ca, and U/Ca) using Holocene samples from the Atlantic and Pacific oceans. We examined chemical variability over a range of test sizes for two surface-dwelling foraminifers (Globigerinoides sacculifer and Globigerinoides ruber). Measurements of δ 11B in G. ruber show no significant relationship with test size in either Atlantic or Pacific sites and appear to provide a robust proxy of surface seawater pH. Likewise there is no significant variability in the δ 11B of our Atlantic core top G. sacculifer, but we find that δ 11B increases with increasing test size for G. sacculifer in the Pacific. These Systematic differences in δ 11B are inferred to be a consequence of isotopically light gametogenic calcite in G. sacculifer and its preferential preservation during postdepositional dissolution. The trace element ratio proxies of ocean Carbonate equilibria, U/Ca and B/Ca, show Systematic increases in both G. ruber and G. sacculifer with increasing test size, possibly as a result of changing growth rates. This behavior complicates their use in paleoceanographic reconstructions. In keeping with several previous studies we find that Mg/Ca ratios increase with increasing size fraction in our well-preserved Atlantic G. sacculifer but not in G. ruber. In contrast to previous interpretations we suggest that these observations reflect a proportionally larger influence of compositionally distinct gametogenic calcite in small individuals compared to larger ones. As with δ 11B this influences G. sacculifer but not G. ruber, which has negligible gametogenic calcite.

  • A core top assessment of proxies for the ocean Carbonate System in surface-dwelling foraminifers
    Paleoceanography, 2007
    Co-Authors: Gavin L. Foster, Daniela N Schmidt, Tim Elliott, Trevor Bailey, Paul Pearson, Brian Haley, Christopher D. Coath
    Abstract:

    We have assessed the reliability of several foraminifer-hosted proxies of the ocean Carbonate System (d11B,\ud B/Ca, and U/Ca) using Holocene samples from the Atlantic and Pacific oceans. We examined chemical\ud variability over a range of test sizes for two surface-dwelling foraminifers (Globigerinoides sacculifer and\ud Globigerinoides ruber). Measurements of d11B in G. ruber show no significant relationship with test size in\ud either Atlantic or Pacific sites and appear to provide a robust proxy of surface seawater pH. Likewise there is no\ud significant variability in the d11B of our Atlantic core top G. sacculifer, but we find that d11B increases with\ud increasing test size for G. sacculifer in the Pacific. These Systematic differences in d11B are inferred to be a\ud consequence of isotopically light gametogenic calcite in G. sacculifer and its preferential preservation during\ud postdepositional dissolution. The trace element ratio proxies of ocean Carbonate equilibria, U/Ca and B/Ca,\ud show Systematic increases in both G. ruber and G. sacculifer with increasing test size, possibly as a result of\ud changing growth rates. This behavior complicates their use in paleoceanographic reconstructions. In keeping\ud with several previous studies we find that Mg/Ca ratios increase with increasing size fraction in our wellpreserved\ud Atlantic G. sacculifer but not in G. ruber. In contrast to previous interpretations we suggest that these\ud observations reflect a proportionally larger influence of compositionally distinct gametogenic calcite in small\ud individuals compared to larger ones. As with d11B this influences G. sacculifer but not G. ruber, which has\ud negligible gametogenic calcite

Tim Elliott - One of the best experts on this subject based on the ideXlab platform.

  • Boron isotopes and B/Ca in benthic foraminifera: proxies for the deep ocean Carbonate System
    Earth and Planetary Science Letters, 2011
    Co-Authors: James W. B. Rae, Gavin L. Foster, Daniela N Schmidt, Tim Elliott
    Abstract:

    Abstract Accurate records of the state of the ocean Carbonate System are critical for understanding past changes in pCO 2 , ocean acidification and climate. The chemical principles underlying the proxy of oceanic pH provided by the boron isotope ratio of foraminiferal Carbonate are relatively well understood, but the proxy's reliability has been questioned. We present 76 new Multi-Collector Inductively-Coupled Plasma Mass Spectrometry (MC-ICPMS) δ 11 B measurements on a range of benthic foraminifera from 23 late-Holocene samples from the Atlantic that reaffirm the utility of the δ 11 B-pH proxy. Our boron isotope measurements on ~ 10 benthic foraminifera tests typically yield a precision of ~ ± 0.25‰ at 2 s.d. (equivalent to ~ ± 0.03 pH units). δ 11 B values of epifaunal species are within analytical uncertainty of those predicted from a simple model assuming sole incorporation of B(OH) 4 − from seawater and no vital effects, using the independently determined fractionation factor of 1.0272 between 11 B/ 10 B of aqueous boron species. Infaunal foraminifera are consistent with this model, but record the combined effects of lower pore-water δ 11 B and pH. No influence of partial dissolution or shell size on δ 11 B is observed. We have also measured the B/Ca ratios of the same samples. For individual Cibicidoides species, B/Ca shows a good correlation with Δ[CO 3 2− ], but the B/Ca of different co-occurring species morphotypes varies considerably. These effects are not seen in δ 11 B, which may therefore provide a more robust proxy of the ocean Carbonate System. Whilst in theory δ 11 B and B/Ca can be combined to provide a quantitative reconstruction of alkalinity and dissolved inorganic Carbonate (DIC), in practice this is precluded by propagated uncertainties. δ 11 B data give significant constraints on foraminifera calcification mechanisms, and seem most simply explained by incorporation of B(OH) 4 − into a HCO 3 − pool, which is then completely incorporated in foraminiferal CaCO 3 . Our demonstration of the predictable variation of δ 11 B with pH, across a wide range of species and locations, provides confidence in the application of MC-ICPMS measurements of foraminiferal δ 11 B to reconstruct past changes in the ocean Carbonate System.

  • A core top assessment of proxies for the ocean Carbonate System in surface‐dwelling foraminifers
    Paleoceanography, 2007
    Co-Authors: Gavin L. Foster, Daniela N Schmidt, Tim Elliott, T. R. Bailey, Paul Nicholas Pearson, Brian A. Haley, Christopher D. Coath
    Abstract:

    We have assessed the reliability of several foraminifer-hosted proxies of the ocean Carbonate System (δ 11B, B/Ca, and U/Ca) using Holocene samples from the Atlantic and Pacific oceans. We examined chemical variability over a range of test sizes for two surface-dwelling foraminifers (Globigerinoides sacculifer and Globigerinoides ruber). Measurements of δ 11B in G. ruber show no significant relationship with test size in either Atlantic or Pacific sites and appear to provide a robust proxy of surface seawater pH. Likewise there is no significant variability in the δ 11B of our Atlantic core top G. sacculifer, but we find that δ 11B increases with increasing test size for G. sacculifer in the Pacific. These Systematic differences in δ 11B are inferred to be a consequence of isotopically light gametogenic calcite in G. sacculifer and its preferential preservation during postdepositional dissolution. The trace element ratio proxies of ocean Carbonate equilibria, U/Ca and B/Ca, show Systematic increases in both G. ruber and G. sacculifer with increasing test size, possibly as a result of changing growth rates. This behavior complicates their use in paleoceanographic reconstructions. In keeping with several previous studies we find that Mg/Ca ratios increase with increasing size fraction in our well-preserved Atlantic G. sacculifer but not in G. ruber. In contrast to previous interpretations we suggest that these observations reflect a proportionally larger influence of compositionally distinct gametogenic calcite in small individuals compared to larger ones. As with δ 11B this influences G. sacculifer but not G. ruber, which has negligible gametogenic calcite.

  • A core top assessment of proxies for the ocean Carbonate System in surface-dwelling foraminifers
    Paleoceanography, 2007
    Co-Authors: Gavin L. Foster, Daniela N Schmidt, Tim Elliott, Trevor Bailey, Paul Pearson, Brian Haley, Christopher D. Coath
    Abstract:

    We have assessed the reliability of several foraminifer-hosted proxies of the ocean Carbonate System (d11B,\ud B/Ca, and U/Ca) using Holocene samples from the Atlantic and Pacific oceans. We examined chemical\ud variability over a range of test sizes for two surface-dwelling foraminifers (Globigerinoides sacculifer and\ud Globigerinoides ruber). Measurements of d11B in G. ruber show no significant relationship with test size in\ud either Atlantic or Pacific sites and appear to provide a robust proxy of surface seawater pH. Likewise there is no\ud significant variability in the d11B of our Atlantic core top G. sacculifer, but we find that d11B increases with\ud increasing test size for G. sacculifer in the Pacific. These Systematic differences in d11B are inferred to be a\ud consequence of isotopically light gametogenic calcite in G. sacculifer and its preferential preservation during\ud postdepositional dissolution. The trace element ratio proxies of ocean Carbonate equilibria, U/Ca and B/Ca,\ud show Systematic increases in both G. ruber and G. sacculifer with increasing test size, possibly as a result of\ud changing growth rates. This behavior complicates their use in paleoceanographic reconstructions. In keeping\ud with several previous studies we find that Mg/Ca ratios increase with increasing size fraction in our wellpreserved\ud Atlantic G. sacculifer but not in G. ruber. In contrast to previous interpretations we suggest that these\ud observations reflect a proportionally larger influence of compositionally distinct gametogenic calcite in small\ud individuals compared to larger ones. As with d11B this influences G. sacculifer but not G. ruber, which has\ud negligible gametogenic calcite

Daniela N Schmidt - One of the best experts on this subject based on the ideXlab platform.

  • Boron isotopes and B/Ca in benthic foraminifera: proxies for the deep ocean Carbonate System
    Earth and Planetary Science Letters, 2011
    Co-Authors: James W. B. Rae, Gavin L. Foster, Daniela N Schmidt, Tim Elliott
    Abstract:

    Abstract Accurate records of the state of the ocean Carbonate System are critical for understanding past changes in pCO 2 , ocean acidification and climate. The chemical principles underlying the proxy of oceanic pH provided by the boron isotope ratio of foraminiferal Carbonate are relatively well understood, but the proxy's reliability has been questioned. We present 76 new Multi-Collector Inductively-Coupled Plasma Mass Spectrometry (MC-ICPMS) δ 11 B measurements on a range of benthic foraminifera from 23 late-Holocene samples from the Atlantic that reaffirm the utility of the δ 11 B-pH proxy. Our boron isotope measurements on ~ 10 benthic foraminifera tests typically yield a precision of ~ ± 0.25‰ at 2 s.d. (equivalent to ~ ± 0.03 pH units). δ 11 B values of epifaunal species are within analytical uncertainty of those predicted from a simple model assuming sole incorporation of B(OH) 4 − from seawater and no vital effects, using the independently determined fractionation factor of 1.0272 between 11 B/ 10 B of aqueous boron species. Infaunal foraminifera are consistent with this model, but record the combined effects of lower pore-water δ 11 B and pH. No influence of partial dissolution or shell size on δ 11 B is observed. We have also measured the B/Ca ratios of the same samples. For individual Cibicidoides species, B/Ca shows a good correlation with Δ[CO 3 2− ], but the B/Ca of different co-occurring species morphotypes varies considerably. These effects are not seen in δ 11 B, which may therefore provide a more robust proxy of the ocean Carbonate System. Whilst in theory δ 11 B and B/Ca can be combined to provide a quantitative reconstruction of alkalinity and dissolved inorganic Carbonate (DIC), in practice this is precluded by propagated uncertainties. δ 11 B data give significant constraints on foraminifera calcification mechanisms, and seem most simply explained by incorporation of B(OH) 4 − into a HCO 3 − pool, which is then completely incorporated in foraminiferal CaCO 3 . Our demonstration of the predictable variation of δ 11 B with pH, across a wide range of species and locations, provides confidence in the application of MC-ICPMS measurements of foraminiferal δ 11 B to reconstruct past changes in the ocean Carbonate System.

  • A core top assessment of proxies for the ocean Carbonate System in surface‐dwelling foraminifers
    Paleoceanography, 2007
    Co-Authors: Gavin L. Foster, Daniela N Schmidt, Tim Elliott, T. R. Bailey, Paul Nicholas Pearson, Brian A. Haley, Christopher D. Coath
    Abstract:

    We have assessed the reliability of several foraminifer-hosted proxies of the ocean Carbonate System (δ 11B, B/Ca, and U/Ca) using Holocene samples from the Atlantic and Pacific oceans. We examined chemical variability over a range of test sizes for two surface-dwelling foraminifers (Globigerinoides sacculifer and Globigerinoides ruber). Measurements of δ 11B in G. ruber show no significant relationship with test size in either Atlantic or Pacific sites and appear to provide a robust proxy of surface seawater pH. Likewise there is no significant variability in the δ 11B of our Atlantic core top G. sacculifer, but we find that δ 11B increases with increasing test size for G. sacculifer in the Pacific. These Systematic differences in δ 11B are inferred to be a consequence of isotopically light gametogenic calcite in G. sacculifer and its preferential preservation during postdepositional dissolution. The trace element ratio proxies of ocean Carbonate equilibria, U/Ca and B/Ca, show Systematic increases in both G. ruber and G. sacculifer with increasing test size, possibly as a result of changing growth rates. This behavior complicates their use in paleoceanographic reconstructions. In keeping with several previous studies we find that Mg/Ca ratios increase with increasing size fraction in our well-preserved Atlantic G. sacculifer but not in G. ruber. In contrast to previous interpretations we suggest that these observations reflect a proportionally larger influence of compositionally distinct gametogenic calcite in small individuals compared to larger ones. As with δ 11B this influences G. sacculifer but not G. ruber, which has negligible gametogenic calcite.

  • A core top assessment of proxies for the ocean Carbonate System in surface-dwelling foraminifers
    Paleoceanography, 2007
    Co-Authors: Gavin L. Foster, Daniela N Schmidt, Tim Elliott, Trevor Bailey, Paul Pearson, Brian Haley, Christopher D. Coath
    Abstract:

    We have assessed the reliability of several foraminifer-hosted proxies of the ocean Carbonate System (d11B,\ud B/Ca, and U/Ca) using Holocene samples from the Atlantic and Pacific oceans. We examined chemical\ud variability over a range of test sizes for two surface-dwelling foraminifers (Globigerinoides sacculifer and\ud Globigerinoides ruber). Measurements of d11B in G. ruber show no significant relationship with test size in\ud either Atlantic or Pacific sites and appear to provide a robust proxy of surface seawater pH. Likewise there is no\ud significant variability in the d11B of our Atlantic core top G. sacculifer, but we find that d11B increases with\ud increasing test size for G. sacculifer in the Pacific. These Systematic differences in d11B are inferred to be a\ud consequence of isotopically light gametogenic calcite in G. sacculifer and its preferential preservation during\ud postdepositional dissolution. The trace element ratio proxies of ocean Carbonate equilibria, U/Ca and B/Ca,\ud show Systematic increases in both G. ruber and G. sacculifer with increasing test size, possibly as a result of\ud changing growth rates. This behavior complicates their use in paleoceanographic reconstructions. In keeping\ud with several previous studies we find that Mg/Ca ratios increase with increasing size fraction in our wellpreserved\ud Atlantic G. sacculifer but not in G. ruber. In contrast to previous interpretations we suggest that these\ud observations reflect a proportionally larger influence of compositionally distinct gametogenic calcite in small\ud individuals compared to larger ones. As with d11B this influences G. sacculifer but not G. ruber, which has\ud negligible gametogenic calcite