Major shifts in calcareous phytoplankton assemblages through the Eocene-Oligocene transition of Tanzania and their implications for low-latitude primary production
Abstract
A high-resolution record of exceptionally well preserved calcareous nannofossil assemblages from
Tanzania is marked by two key transitions closely related to the climatic events of the Eocene-Oligocene
transition (EOT). The first transition, at 34.0 Ma, precedes the first positive shift in d18O and coincides with a
distinct interval of very low nannofossil abundance and a cooling in sea surface temperatures (SST). The second,
at 33.63 Ma, is immediately above the Eocene-Oligocene boundary (EOB) and is associated with a significant
drop in nannofossil diversity. Both transitions involve significant reductions in the abundance of holococcoliths
and other oligotrophic taxa. These changes in calcareous phytoplankton assemblages indicate (1) a widespread
and significant perturbation to the low-latitude surface ocean closely tied to the EOB, (2) a potential role for
reduced carbonate primary production at the onset of global cooling, and (3) a significant increase in nutrient
availability in the low-latitude surface ocean through the EOT.