Sodium-Calcium Ratios in the Planktic Foraminifera Trilobatus Sacculifer as a Proxy for Sea Surface Salinity

• Main Author: Watkins, Colton Steele
• Format: Thesis
• Language: unknown
• Published: Old Dominion University Libraries 2020
• Subjects: Lynch; North Atlantic
• Online Access: https://dx.doi.org/10.25777/f7xb-yg22; https://digitalcommons.odu.edu/oeas_etds/176/

Recent culture and field studies have found a significant positive correlation between seawater salinity and the incorporation of sodium into foraminiferal calcite, suggesting a potential new proxy for reconstructing past changes in sea surface salinity (SSS) (Mezger et al., 2016 and Bertlich et al., 2018). In order to test the applicability of this new proxy in an open-ocean setting, Na/Ca ratios in the planktic foraminifera Trilobatus sacculifer (T. sacculifer Na/Ca) were measured from a suite of sediment core tops spanning a natural salinity gradient from the North Atlantic subtropical gyre to the South Atlantic subtropical gyre. Initial results from nine core tops spanning a salinity range of 1.6 show a positive correlation between upper water column salinity and T. sacculifer Na/Ca (R2 = 0.81, p < 0.005). The data also suggest there is no relationship between T. sacculifer Na/Ca and shell weight, shell size, or habitat temperature, indicating that shell Na/Ca may be predominantly controlled by salinity. In addition, we generated a high-resolution downcore record of T. sacculifer Na/Ca variability over the last deglaciation from Florida Straits core JPC26. Results show good agreement between our new Na/Ca record with the previously published deglacial δ18Osw record that is also thought to reflect SSS variability from the same core (Schmidt and Lynch-Stieglitz, 2011). Both records indicate an abrupt increase in SSS during the Younger Dryas (11.7 – 12.9 kyr). Converting our new JPC26 T. sacculifer Na/Ca ratios to SSS using our Atlantic core top calibration indicates a maximum salinity change of ~2.2 across the last deglaciation.