- Email: [email protected]
Algal constraints on the cenozoic history of atmospheric CO2
A244
Goldschmidt Conference Abstracts 2006
d44/42 Ca in gas hydrates, porewaters and authigenic carbonates from Niger Delta sediments
Algal constraints on the cenozoic history of atmospheric CO2 J. HENDERIKS1, R. RICKABY2, H. ELDERFIELD3
G.M. HENDERSON1, N.-C. CHU1, G. BAYON2, M. BENOIT3
1
Deparment of Geology and Geochemistry, Stockholm University, SE-106 91 Stockholm, Sweden (jorijntje.henderiks @geo.su.se) 2 Department of Earth Sciences, University of Oxford, Oxford OX1 3PR, UK ([email protected]) 3 Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK ([email protected]) Future acidification of the oceans due to raised carbon dioxide levels will cause a drastic change in ocean chemistry that has not been experienced for at least the last 650,000 years, and will likely reduce marine calcification. Coccolithophores, calcareous haptophyte algae, constitute a key biological group subjected to this global process. The rate at which the natural populations can acclimatise or adapt to changes in ocean chemistry is an essential factor in how their natural feedback mechanisms will operate in future. Novel experiments testing the environmental tolerance of different extant coccolithophore species to various conditions of seawater carbonate chemistry reveal the need to consider species-specific effects when evaluating whole ecosystem responses to elevated pCO2 (Langer, 2006). Specifically, PIC/POC ratios in Coccolithus pelagicus appeared unaffected by the range in CO2 tested (Langer, 2006), which to date remains unexplained. We argue that the evolutionary history of the Coccolithus genus, which originated in the early Paleocene, holds not only invaluable information on how species evolve within ‘planktic super-species’ (de Vargas, 2004) whilst keeping rather conservative coccolith morphologies, as will be demonstrated. It potentially is also a crucial factor in constraining maximum levels of atmospheric CO2 experienced in the geological past.
1
Department of Earth Sciences, University of Oxford, Oxford OX1 3PR, UK ([email protected] ; nanchin@ earth. ox.ac.uk) 2 De´partement Ge´osciences Marines, IFREMER, 29280 Plouzane´, France ([email protected]) 3 IUEM, Place Nicolas Copernic, 29280 Plouzane´, France ([email protected]) We report Ca isotope ratios for gas hydrates, porewaters and authigenic carbonate concretions recovered by coring at cold seep locations from the Niger delta deep province. Our aim in this study has been to understand the mechanisms controlling Ca-isotope fractionation during biogeochemical processes at cold seeps. Carbonate precipitation in cold seep environments is closely related to the anaerobic oxidation of methane (AOM), which is mediated by a consortium of micro-organisms and releases bicarbonate ðHCO3 and sulfide (HS) into surrounding porewaters (Bayon, in review). We found that carbonate precipitation causes 44 Ca enrichment in the surrounding porewaters, as expected from previous work demonstrating that calcite prefers isotopically light Ca (Gussone, 2005). Our measured d44/42Ca values for porewaters are consistent with values estimated previously by Teichert et al. (2005). In our studied sediment cores, the highest d44/42Ca ratios in porewaters were measured at the AOM sediment depth (dashed line in Fig. 1), indicating on-going carbonate formation at these horizons. Porewater and carbonate d44/42Ca measurements may therefore offer potential to identify the location and intensity of AOM processes now and in the past. We will also discuss the mineralogical control of Ca isotope fractionation at cold seeps.
References de Vargas, C. et al., 2004. Super-species in calcareous plankton. In: Thierstein, H.R., Young, J.R. (Eds.), Coccolithophores: From Molecular Processes to Global Impact. Springer-Verlag, pp. 271–298. Langer, G., et al., 2006. The response of Calcidiscus leptoporus and Coccolithus pelagicus to changing carbonate chemistry of seawater. Geophysical Research Abstracts 8, Sref-ID: 1607-962/gra/EGU06-A05161. doi:10.1016/j.gca.2006.06.492 Fig. 1. d44/42Ca, Mg/Ca and Sr/Ca of carbonates porewaters and gas hydrates from core N2-KS44.
References Bayon, G., et al., in review. Geochim. Cosmochim. Acta. Gussone, G. et al., 2005. Geochim. Cosmochim. Acta 69 (18), 4485–4494. Teichert, B.M.A., Gussone, A., Bohrmann, G., 2005. Geology 33 (3), 213– 216. doi:10.1016/j.gca.2006.06.493
Goldschmidt Conference Abstracts 2006
d44/42 Ca in gas hydrates, porewaters and authigenic carbonates from Niger Delta sediments
Algal constraints on the cenozoic history of atmospheric CO2 J. HENDERIKS1, R. RICKABY2, H. ELDERFIELD3
G.M. HENDERSON1, N.-C. CHU1, G. BAYON2, M. BENOIT3
1
Deparment of Geology and Geochemistry, Stockholm University, SE-106 91 Stockholm, Sweden (jorijntje.henderiks @geo.su.se) 2 Department of Earth Sciences, University of Oxford, Oxford OX1 3PR, UK ([email protected]) 3 Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK ([email protected]) Future acidification of the oceans due to raised carbon dioxide levels will cause a drastic change in ocean chemistry that has not been experienced for at least the last 650,000 years, and will likely reduce marine calcification. Coccolithophores, calcareous haptophyte algae, constitute a key biological group subjected to this global process. The rate at which the natural populations can acclimatise or adapt to changes in ocean chemistry is an essential factor in how their natural feedback mechanisms will operate in future. Novel experiments testing the environmental tolerance of different extant coccolithophore species to various conditions of seawater carbonate chemistry reveal the need to consider species-specific effects when evaluating whole ecosystem responses to elevated pCO2 (Langer, 2006). Specifically, PIC/POC ratios in Coccolithus pelagicus appeared unaffected by the range in CO2 tested (Langer, 2006), which to date remains unexplained. We argue that the evolutionary history of the Coccolithus genus, which originated in the early Paleocene, holds not only invaluable information on how species evolve within ‘planktic super-species’ (de Vargas, 2004) whilst keeping rather conservative coccolith morphologies, as will be demonstrated. It potentially is also a crucial factor in constraining maximum levels of atmospheric CO2 experienced in the geological past.
1
Department of Earth Sciences, University of Oxford, Oxford OX1 3PR, UK ([email protected] ; nanchin@ earth. ox.ac.uk) 2 De´partement Ge´osciences Marines, IFREMER, 29280 Plouzane´, France ([email protected]) 3 IUEM, Place Nicolas Copernic, 29280 Plouzane´, France ([email protected]) We report Ca isotope ratios for gas hydrates, porewaters and authigenic carbonate concretions recovered by coring at cold seep locations from the Niger delta deep province. Our aim in this study has been to understand the mechanisms controlling Ca-isotope fractionation during biogeochemical processes at cold seeps. Carbonate precipitation in cold seep environments is closely related to the anaerobic oxidation of methane (AOM), which is mediated by a consortium of micro-organisms and releases bicarbonate ðHCO3 and sulfide (HS) into surrounding porewaters (Bayon, in review). We found that carbonate precipitation causes 44 Ca enrichment in the surrounding porewaters, as expected from previous work demonstrating that calcite prefers isotopically light Ca (Gussone, 2005). Our measured d44/42Ca values for porewaters are consistent with values estimated previously by Teichert et al. (2005). In our studied sediment cores, the highest d44/42Ca ratios in porewaters were measured at the AOM sediment depth (dashed line in Fig. 1), indicating on-going carbonate formation at these horizons. Porewater and carbonate d44/42Ca measurements may therefore offer potential to identify the location and intensity of AOM processes now and in the past. We will also discuss the mineralogical control of Ca isotope fractionation at cold seeps.
References de Vargas, C. et al., 2004. Super-species in calcareous plankton. In: Thierstein, H.R., Young, J.R. (Eds.), Coccolithophores: From Molecular Processes to Global Impact. Springer-Verlag, pp. 271–298. Langer, G., et al., 2006. The response of Calcidiscus leptoporus and Coccolithus pelagicus to changing carbonate chemistry of seawater. Geophysical Research Abstracts 8, Sref-ID: 1607-962/gra/EGU06-A05161. doi:10.1016/j.gca.2006.06.492 Fig. 1. d44/42Ca, Mg/Ca and Sr/Ca of carbonates porewaters and gas hydrates from core N2-KS44.
References Bayon, G., et al., in review. Geochim. Cosmochim. Acta. Gussone, G. et al., 2005. Geochim. Cosmochim. Acta 69 (18), 4485–4494. Teichert, B.M.A., Gussone, A., Bohrmann, G., 2005. Geology 33 (3), 213– 216. doi:10.1016/j.gca.2006.06.493