NOAA/WDS Paleoclimatology - South Atlantic Coccolith Assemblage and Morphology Data from the Early Oligocene

Early Oligocene global climate was characterized by initiated Antarctic glaciation and meridional overturning circulation, which then led to profound eutrophication in the upper ocean. Generating a high-resolution coccolith record help to understand the responses of the marine phytoplankton to the newly established environment. Using highly resolved (~6 kyr time-resolution) marine sediment samples from Deep Sea Drilling Project Site 522 in the South Atlantic Ocean, we conducted a comprehensive morphologic study on coccoliths from the genera Reticulofenestra, Dictyococcites and Coccolithus, that dominated the interval between ~33.1 to 32.8 Ma. Our results showed that the size variations of three measured genera are significantly correlated (p<0.01) to each other, indicating homogeneous responses to the environmental changes. Moreover, spectrum analysis on integrated morphologic data of all measured coccoliths showed distinct obliquity (~40-kyr) and precession (~23-kyr and ~18-kyr) cycles. We suggest that these variations were mainly driven by temperate, short-term ecological fluctuations, which periodically altered the nutrient condition in the common living habitats for the studied coccolithophores. We proposed two tentative explanations focusing on the obliquity signal. First, the cyclic variation could result from obliquity-modulated ice volume changes and variations in ocean circulation intensity, which influenced nutrient export from deep waters to the upper ocean. Alternatively, the changes in coccolith size may indicate the strength of seasonality that influenced the upper ocean mixing on the west coast of South Africa.