DID NON-FOSSILIZING PLANKTON RULE THE OCEANS AFTER THE END CRETACEOUS MASS EXTINCTION?

Our oceans are being stressed by warming and acidification, impacting complex systems such as primary production and the global carbon cycle. How marine life will react to this ongoing long-term change is unknown. Using the geological record, we can provide natural analogies for both present and future changes in the oceans.

The K-Pg extinction event, 66 million years ago, was associated with a major reduction in oceanic productivity, including the extinction of 93% of calcareous nannoplankton species, resulting in major disruption to food chains and the carbon cycle. So far, our understanding of how the oceans recovered from this disturbance has been limited to studies of plankton that produce a fossil record leaving a large portion of ancient plankton ecosystems unstudied.

In this project we are working together to develop a more complete record of plankton diversity by combining biomarkers for non-fossilizing plankton with diversity records of planktic foraminifera and nannofossils to gain a fuller picture of how the oceans recovered following the K-Pg extinction event. Here, we will present preliminary planktic foraminifera counts from our sites in Tunisia. These records over the course of this study will be added to with additional plankton diversity records from Spain and the US Gulf Coast to test the hypothesis that non-fossilizing phytoplankton dominated the oceans in the aftermath of the K-Pg extinction and that shifts in populations of non-fossilizing plankton are associated with shifts in the population of fossilizing plankton. In particular, we hypothesize that acme events of planktic foraminifera (which serve as a proxy for the larger zooplankton community) are associated with changes in the dominant phytoplankton type. We will use data from our localities to compare oceanic responses on both local and regional scales following major global disruption. This study will not only allow us to reconstruct the response of the whole plankton ecosystem to global change but will provide insights into potential changes in modern oceans because of anthropogenic driven change.