Planktonic foraminifera luminescence as a new paleoclimate proxy for oceanic and atmospheric conditions off South America

Luminescence emitted by minerals has long been used in paleoenvironmental studies, particularly thermoluminescence (TL) from carbonates. TL emission in calcite is controlled by the type and quantity of defects in the crystal lattice, which may act as charge traps and/or recombination centers. These defects can be influenced by environmental conditions prevailing at the time of crystallization, for example through the incorporation of impurities substituting calcium in the calcite lattice (e.g., Mg, Mn, Fe). In this context, this study investigates the potential of TL signals emitted from the calcite of the planktonic foraminifera Globigerinoides ruber (white sensu stricto, 250–350 μm) as a paleoclimate proxies. This species was selected due to its widespread use in paleoclimate reconstructions, high abundance, and known sensitivity to environmental variability. We analyzed samples from three marine sediment cores from the western Atlantic, encompassing different spatial and temporal contexts. Two cores represent modern conditions under contrasting oceanographic settings: MD23-3669MC (equatorial Atlantic) and GeoB6211-1 (subtropical South Atlantic). The third core, CDH-89 (equatorial Atlantic), spans the penultimate glacial–interglacial transition (143–122 ka), allowing the comparison between modern and paleoclimatic signal.

The resulting TL intensity curves (light emitted per unit mass and unit radiation dose) exhibit peaks at approximately 65°C and 400°C. These TL signals were compared with classical paleoceanographic proxies, i.e., Mg/Ca, Mn/Ca, Fe/Ca and stable isotope data, measured on shells of the same planktonic foraminifera species. Principal component analysis indicates that the 400°C peak is primarily controlled by sea surface temperature variations, whereas the 65°C peak is associated with proxies related to continental input to the ocean. These results demonstrate that TL signals in planktonic foraminifera preserve environmental signatures, supporting their potential as new paleoclimate proxies. Further systematic testing across environments and experimental conditions is required to fully validate and advance these proxies for broader paleoenvironmental applications.