Salinity and temperature determine seawater density, and differences in both thereby control global thermohaline circulation. Whereas numerous proxies have been calibrated and applied to reconstruct temperature, a direct and independent proxy for salinity is still missing. Ideally, a new proxy for salinity should target one of the direct constituents of dissolved salt, such as [Na+] or [Cl−]. This study investigates the impact of salinity on foraminiferal Na/Ca values by laser ablation ICP-MS analyses of specimens of the benthic foraminifer Ammonia tepida cultured at a range of salinities (30.0-38.6). Foraminifera at lower salinities (30.0 and 32.5) added more chambers (10-11) to their test over the course of the culturing experiment than those maintained at higher salinities (36.1, 7-8 chambers, and 38.6, 6-7 chambers), suggesting that growth rates in this species are promoted by lower salinities. The Na/Ca of cultured specimens correlates significantly with seawater salinity (Na/Ca Combining double low line 0.22S-0.75, R 2 Combining double low line 0.96, p < 0.01) and size. Values for Na/Ca and Dlt;/igt;Na vary between 5.17 and 9.29 mmol mol-1 and 0.12-0.16 times; 10-3, which are similar to values from inorganic precipitation experiments. The significant correlation between test size and Na/Ca results from co-variation with salinity. This implies that foraminiferal Na/Ca could serve as a robust and independent proxy for salinity, enabling salinity reconstructions independent of calcitic delta;18O. © 2013 Author(s).
CITATION STYLE
Wit, J. C., De Nooijer, L. J., Wolthers, M., & Reichart, G. J. (2013). A novel salinity proxy based on na incorporation into foraminiferal calcite. Biogeosciences, 10(10), 6375–6387. https://doi.org/10.5194/bg-10-6375-2013
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