Planktonic foraminifera as a tool of past seasonality reconstruction

Seasonal changes in seawater temperature leave large imprints on the stable oxygen isotope composition (δ¹⁸O) of planktonic foraminiferal tests, based on which the past seasonal changes can be reconstructed. However, there are still problems needed to be figured out in regard to this new method, to improve the reliability of seasonality reconstruction. For example, the selected foraminiferal species, the used size fraction, and the sample area. As a result, by analyzing planktonic foraminiferal test δ¹⁸O from the sediment trap samples deployed in the South China Sea, we found that foraminiferal seasonal δ¹⁸O signal is strongly distorted (amplified or damped) by seasonal variations in their habitat depth, particularly for the species living in low latitude. Furthermore, Globigerinoides ruber of 300-355 um can record the most comprehensive seawater seasonality information. This study provides strong support to the reconstruction of past seawater seasonal temperature by using individual planktonic foraminifera.