Objective:

To extend the culture-based magnesium-to-calcium temperature calibration of the planktonic foraminifer Globigerina bulloides down to 6 °C for improved cold-ocean reconstructions.

Key Findings:

• Magnesium-to-calcium ratios showed a positive exponential relationship with temperature across the 6 to 13 °C range.
• Sodium-to-calcium ratios varied systematically with temperature but in the opposite direction.
• No significant relationship was found between elemental ratios and salinity.
• Sodium-to-calcium and strontium-to-calcium ratios responded to carbonate ion concentration at constant pH, but in opposite directions.

Interpretation:

Limitations:

• Most existing calibrations were developed above 14 °C, limiting their applicability to colder waters.

Conclusion: