Sodium incorporation in foraminiferal calcite: An evaluation of the Na/Ca salinity proxy and evidence for multiple Na-bearing phases
The ratio of sodium to calcium (Na/Ca) in foraminiferal calcite has been proposed as a proxy for salinity, yet relatively little is known about the incorporation of sodium into the shells of foraminifera. Ongoing debates include the location of Na in the calcite crystal lattice, the possibility that...
Published in: | Geochimica et Cosmochimica Acta |
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ftgfzpotsdam:oai:gfzpublic.gfz-potsdam.de:item_5017639 2023-06-18T03:42:47+02:00 Sodium incorporation in foraminiferal calcite: An evaluation of the Na/Ca salinity proxy and evidence for multiple Na-bearing phases Gray, W. Evans, D. Henehan, M. Weldeab, S. Lea, D. Müller, W. Rosenthal, Y. 2023 https://gfzpublic.gfz-potsdam.de/pubman/item/item_5017639 unknown info:eu-repo/semantics/altIdentifier/doi/10.1016/j.gca.2023.03.011 https://gfzpublic.gfz-potsdam.de/pubman/item/item_5017639 Geochimica et Cosmochimica Acta info:eu-repo/semantics/article 2023 ftgfzpotsdam https://doi.org/10.1016/j.gca.2023.03.011 2023-06-04T23:39:40Z The ratio of sodium to calcium (Na/Ca) in foraminiferal calcite has been proposed as a proxy for salinity, yet relatively little is known about the incorporation of sodium into the shells of foraminifera. Ongoing debates include the location of Na in the calcite crystal lattice, the possibility that at least some Na might be complexed with organics, and the influence of spines/spine bases. We present new Na/Ca measurements, determined using both solution and laser ablation ICP-MS, of the planktonic foraminifera Globigerinoides ruber (white) from plankton tows and sediment traps spanning a wide salinity range (32.5–40.7 salinity units), laboratory cultures under varying carbonate chemistry, and globally-distributed core-top samples. Our results show that Na/Ca in recently living foraminifera measured by laser ablation ICP-MS is elevated by up to 5 mmol/mol (∼85%) relative to the same samples measured by solution ICP-MS (the same comparison for Mg/Ca shows excellent agreement between the techniques). Na/Ca in recently living foraminifera measured by laser ablation ICP-MS displays a significant relationship with salinity above ∼36 salinity units with a slope of ∼0.7 mmol/mol/salinity unit; however, only a weak relationship is observed between salinity and Na/Ca measured by solution ICP-MS. We propose that Na is incorporated in at least two discrete phases; a primary phase within the CaCO3 mineral, and a (or likely multiple) secondary phase(s). Possibilities for these secondary phases include residual metastable CaCO3, fluid inclusions, high Na/Ca spine bases, and organics. These secondary phases contribute to spatially-resolved analyses (i.e. laser ablation ICP-MS) of recently living foraminifera but are removed by crushing/oxidative cleaning for solution ICP-MS, and during early diagenesis, as evidenced by the agreement between laser analysis of coretop samples and Na/Ca measured by solution. The amount of one of these secondary phases, or the amount of Na within this phase, appears to vary as a function of ... Article in Journal/Newspaper Planktonic foraminifera GFZpublic (German Research Centre for Geosciences, Helmholtz-Zentrum Potsdam) Geochimica et Cosmochimica Acta 348 152 164 |
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Open Polar |
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GFZpublic (German Research Centre for Geosciences, Helmholtz-Zentrum Potsdam) |
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ftgfzpotsdam |
language |
unknown |
description |
The ratio of sodium to calcium (Na/Ca) in foraminiferal calcite has been proposed as a proxy for salinity, yet relatively little is known about the incorporation of sodium into the shells of foraminifera. Ongoing debates include the location of Na in the calcite crystal lattice, the possibility that at least some Na might be complexed with organics, and the influence of spines/spine bases. We present new Na/Ca measurements, determined using both solution and laser ablation ICP-MS, of the planktonic foraminifera Globigerinoides ruber (white) from plankton tows and sediment traps spanning a wide salinity range (32.5–40.7 salinity units), laboratory cultures under varying carbonate chemistry, and globally-distributed core-top samples. Our results show that Na/Ca in recently living foraminifera measured by laser ablation ICP-MS is elevated by up to 5 mmol/mol (∼85%) relative to the same samples measured by solution ICP-MS (the same comparison for Mg/Ca shows excellent agreement between the techniques). Na/Ca in recently living foraminifera measured by laser ablation ICP-MS displays a significant relationship with salinity above ∼36 salinity units with a slope of ∼0.7 mmol/mol/salinity unit; however, only a weak relationship is observed between salinity and Na/Ca measured by solution ICP-MS. We propose that Na is incorporated in at least two discrete phases; a primary phase within the CaCO3 mineral, and a (or likely multiple) secondary phase(s). Possibilities for these secondary phases include residual metastable CaCO3, fluid inclusions, high Na/Ca spine bases, and organics. These secondary phases contribute to spatially-resolved analyses (i.e. laser ablation ICP-MS) of recently living foraminifera but are removed by crushing/oxidative cleaning for solution ICP-MS, and during early diagenesis, as evidenced by the agreement between laser analysis of coretop samples and Na/Ca measured by solution. The amount of one of these secondary phases, or the amount of Na within this phase, appears to vary as a function of ... |
format |
Article in Journal/Newspaper |
author |
Gray, W. Evans, D. Henehan, M. Weldeab, S. Lea, D. Müller, W. Rosenthal, Y. |
spellingShingle |
Gray, W. Evans, D. Henehan, M. Weldeab, S. Lea, D. Müller, W. Rosenthal, Y. Sodium incorporation in foraminiferal calcite: An evaluation of the Na/Ca salinity proxy and evidence for multiple Na-bearing phases |
author_facet |
Gray, W. Evans, D. Henehan, M. Weldeab, S. Lea, D. Müller, W. Rosenthal, Y. |
author_sort |
Gray, W. |
title |
Sodium incorporation in foraminiferal calcite: An evaluation of the Na/Ca salinity proxy and evidence for multiple Na-bearing phases |
title_short |
Sodium incorporation in foraminiferal calcite: An evaluation of the Na/Ca salinity proxy and evidence for multiple Na-bearing phases |
title_full |
Sodium incorporation in foraminiferal calcite: An evaluation of the Na/Ca salinity proxy and evidence for multiple Na-bearing phases |
title_fullStr |
Sodium incorporation in foraminiferal calcite: An evaluation of the Na/Ca salinity proxy and evidence for multiple Na-bearing phases |
title_full_unstemmed |
Sodium incorporation in foraminiferal calcite: An evaluation of the Na/Ca salinity proxy and evidence for multiple Na-bearing phases |
title_sort |
sodium incorporation in foraminiferal calcite: an evaluation of the na/ca salinity proxy and evidence for multiple na-bearing phases |
publishDate |
2023 |
url |
https://gfzpublic.gfz-potsdam.de/pubman/item/item_5017639 |
genre |
Planktonic foraminifera |
genre_facet |
Planktonic foraminifera |
op_source |
Geochimica et Cosmochimica Acta |
op_relation |
info:eu-repo/semantics/altIdentifier/doi/10.1016/j.gca.2023.03.011 https://gfzpublic.gfz-potsdam.de/pubman/item/item_5017639 |
op_doi |
https://doi.org/10.1016/j.gca.2023.03.011 |
container_title |
Geochimica et Cosmochimica Acta |
container_volume |
348 |
container_start_page |
152 |
op_container_end_page |
164 |
_version_ |
1769008850798641152 |