NETWORK ANALYSIS OF THE MARINE MICROPALEONTOLOGICAL RECORD (PART 2): LATE CENOZOIC COOLING RESTRUCTURED GLOBAL MARINE PLANKTON COMMUNITIES

The geographic ranges of marine plankton, including planktonic foraminifera, diatoms, and dinoflagellates, are already shifting poleward due to climate change. However, the extent to which plankton will shift, or if these poleward range extirpations will lead to extinction is unclear. Understanding the development of marine biodiversity patterns over geological time and the factors that influence them are key to contextualizing these current trends.

The fossil record of the macroperforate planktonic foraminifera provides a rich and phylogenetically resolved dataset that provides unique opportunities for understanding marine biogeography dynamics. In particular, we focus on discrete ecogroups and morphogroups that are represented within the Cenozoic planktonic foraminiferal record. We employ bipartite network metrics to quantify latitudinal specialization, and latitudinal equitability for planktonic foraminifera over the last 8 Ma using Triton, a recently developed high-resolution global dataset of planktonic foraminiferal occurrences.

Our results indicate that a global, clade-wide equatorward shift in ecological and morphological communities occurred across the last ~8 million years in response to temperature changes during late Cenozoic bipolar cryosphere formation. Collectively, the Triton data indicate the presence of a “latitudinal equitability gradient” (LEG) amongst planktonic foraminiferal functional groups (in particular, the ecogroups) which is only coupled to the latitudinal biodiversity gradient only through the past ~1 Ma. Prior to this time, LEGs indicate that higher latitudes promoted community equitability across ecological and morphological groups. The biogeographic dynamics of planktonic foraminifera within the recent geological past predict the poleward expansion of global marine trophic levels under even the most conservative future global warming scenarios.