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Seawater nutrient and carbonate ion concentrations recorded as P/Ca, Ba/Ca, and U/Ca in the deep-sea coral D. dianthus

Seawater nutrient and carbonate ion concentrations recorded as P/Ca, Ba/Ca, and U/Ca in the deep-sea coral D. dianthus
Seawater nutrient and carbonate ion concentrations recorded as P/Ca, Ba/Ca, and U/Ca in the deep-sea coral D. dianthus
As paleoceanographic archives, deep sea coral skeletons offer the potential for high temporal resolution and precise absolute dating, but have not been fully investigated for geochemical reconstructions of past ocean conditions. Here we assess the utility of skeletal P/Ca, Ba/Ca and U/Ca in the deep sea coral D. dianthus as proxies of dissolved phosphate (remineralized at shallow depths), dissolved barium (trace element with silicate-type distribution) and carbonate ion concentrations, respectively. Measurements of these proxies in globally distributed D. dianthus specimens show clear dependence on corresponding seawater properties. Linear regression fits of mean coral Element/Ca ratios against seawater properties yield the equations: P/Cacoral (lmol/mol) = (0.6 ± 0.1) P/Casw(lmol/mol) – (23 ± 18), R2 = 0.6, n = 16 and Ba/Cacoral(lmol/mol) = (1.4 ± 0.3) Ba/Casw(lmol/mol) + (0 ± 2), R2 = 0.6, n = 17; no significant relationship is observed between the residuals of each regression and seawater temperature, salinity, pressure, pH or carbonate ion concentrations, suggesting that these variables were not significant secondary dependencies of these proxies. Four D. dianthus specimens growing at locations withOarag 6 0.6 displayed markedly depleted P/Ca compared to the regression based on the remaining samples, a behavior attributed to an undersaturation effect. These corals were excluded from the calibration. Coral U/Ca correlates with seawater carbonate ion: U/Cacoral(lmol/mol) = (?0.016 ± 0.003) ½CO2? 3 ? (lmol/kg) + (3.2 ± 0.3), R2 = 0.6, n = 17. The residuals of the U/Ca calibration are not significantly related to temperature, salinity, or pressure. Scatter about the linear calibration lines is attributed to imperfect spatialtemporal matches between the selected globally distributed specimens and available water column chemical data, and potentially to unresolved additional effects. The uncertainties of these initial proxy calibration regressions predict that dissolved phosphate could be reconstructed to ±0.4 lmol/kg (for 1.3–1.9 lmol/kg phosphate), and dissolved Ba to ±19 nmol/kg (for 41–82 nmol/kg Basw). Carbonate ion concentration derived from U/Ca has an uncertainty of ±31lmol/kg (for 60–120 lmol=kg CO2? 3 ). The effect of microskeletal variability on P/Ca, Ba/Ca, and U/Ca was also assessed, with emphasis on centers of calcification, Fe–Mn phases, and external contaminants. Overall, the results show strong potential for reconstructing aspects of water mass mixing and biogeochemical processes in intermediate and deep waters using fossil deep-sea corals.
0016-7037
2529-2543
Anagnostou, Eleni
4527c274-f765-44ce-89ab-0e437aa3d870
Sherrell, Robert M.
251b287a-1ac0-48aa-a422-edeed2427c22
Gagnon, Alex
6280425b-4886-44b9-b3fa-4f062f36c307
LaVigne, Michele
4a8edeee-b822-4adb-b0d0-1ccb4e10fad1
Field, M. Paul
7f1f876d-21f9-4ed2-b317-24fa267081df
McDonough, William F.
f8f86fb4-274e-4e6a-bd46-15a31d976d6a
Anagnostou, Eleni
4527c274-f765-44ce-89ab-0e437aa3d870
Sherrell, Robert M.
251b287a-1ac0-48aa-a422-edeed2427c22
Gagnon, Alex
6280425b-4886-44b9-b3fa-4f062f36c307
LaVigne, Michele
4a8edeee-b822-4adb-b0d0-1ccb4e10fad1
Field, M. Paul
7f1f876d-21f9-4ed2-b317-24fa267081df
McDonough, William F.
f8f86fb4-274e-4e6a-bd46-15a31d976d6a

Anagnostou, Eleni, Sherrell, Robert M., Gagnon, Alex, LaVigne, Michele, Field, M. Paul and McDonough, William F. (2011) Seawater nutrient and carbonate ion concentrations recorded as P/Ca, Ba/Ca, and U/Ca in the deep-sea coral D. dianthus. Geochimica et Cosmochimica Acta, 75, 2529-2543. (doi:10.1016/j.gca.2011.02.019).

Record type: Article

Abstract

As paleoceanographic archives, deep sea coral skeletons offer the potential for high temporal resolution and precise absolute dating, but have not been fully investigated for geochemical reconstructions of past ocean conditions. Here we assess the utility of skeletal P/Ca, Ba/Ca and U/Ca in the deep sea coral D. dianthus as proxies of dissolved phosphate (remineralized at shallow depths), dissolved barium (trace element with silicate-type distribution) and carbonate ion concentrations, respectively. Measurements of these proxies in globally distributed D. dianthus specimens show clear dependence on corresponding seawater properties. Linear regression fits of mean coral Element/Ca ratios against seawater properties yield the equations: P/Cacoral (lmol/mol) = (0.6 ± 0.1) P/Casw(lmol/mol) – (23 ± 18), R2 = 0.6, n = 16 and Ba/Cacoral(lmol/mol) = (1.4 ± 0.3) Ba/Casw(lmol/mol) + (0 ± 2), R2 = 0.6, n = 17; no significant relationship is observed between the residuals of each regression and seawater temperature, salinity, pressure, pH or carbonate ion concentrations, suggesting that these variables were not significant secondary dependencies of these proxies. Four D. dianthus specimens growing at locations withOarag 6 0.6 displayed markedly depleted P/Ca compared to the regression based on the remaining samples, a behavior attributed to an undersaturation effect. These corals were excluded from the calibration. Coral U/Ca correlates with seawater carbonate ion: U/Cacoral(lmol/mol) = (?0.016 ± 0.003) ½CO2? 3 ? (lmol/kg) + (3.2 ± 0.3), R2 = 0.6, n = 17. The residuals of the U/Ca calibration are not significantly related to temperature, salinity, or pressure. Scatter about the linear calibration lines is attributed to imperfect spatialtemporal matches between the selected globally distributed specimens and available water column chemical data, and potentially to unresolved additional effects. The uncertainties of these initial proxy calibration regressions predict that dissolved phosphate could be reconstructed to ±0.4 lmol/kg (for 1.3–1.9 lmol/kg phosphate), and dissolved Ba to ±19 nmol/kg (for 41–82 nmol/kg Basw). Carbonate ion concentration derived from U/Ca has an uncertainty of ±31lmol/kg (for 60–120 lmol=kg CO2? 3 ). The effect of microskeletal variability on P/Ca, Ba/Ca, and U/Ca was also assessed, with emphasis on centers of calcification, Fe–Mn phases, and external contaminants. Overall, the results show strong potential for reconstructing aspects of water mass mixing and biogeochemical processes in intermediate and deep waters using fossil deep-sea corals.

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Published date: 2011
Organisations: Geochemistry

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Local EPrints ID: 339949
URI: https://eprints.soton.ac.uk/id/eprint/339949
ISSN: 0016-7037
PURE UUID: a43e4451-4a53-4378-9d74-a0c67de7405c

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Date deposited: 06 Jun 2012 10:33
Last modified: 11 Nov 2019 21:02

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