PLIOCENE-PLEISTOCENE TRANSITION: UNRAVELING THE BIOGEOGRAPHY AND FUNCTIONAL DYNAMICS OF PLANKTONIC FORAMINIFERA

The ocean is increasingly affected by anthropogenic climate change. Yet, our understanding of how marine organisms will respond to future environmental perturbations, specifically in terms of latitudinal and functional diversity shifts, remains elusive. Throughout the Pliocene-Pleistocene transition, our planet underwent diverse climate regimes and substantial reconfigurations of global ocean circulation. This period offers a compelling opportunity to enhance our understanding of marine organisms' responses to these varied climate conditions. Planktonic foraminifera are exemplary model organisms that allow us to investigate biogeographic and functional dynamics within marine plankton communities.

In this study, we investigate the exceptional record of planktonic foraminifera using the Triton database from the Pliocene to the Pleistocene (3.9-1.8 Ma). Utilizing bipartite networks, we evaluated the biogeographic shifts of ecological and morphological groups across global, regional, and hemispheric scales during cooling and warming periods. In addition, we examined whether changes in the functional and taxonomic diversity of planktonic foraminifera over time correspond with climate change events to identify the primary environmental drivers behind these patterns.

We document a common long-term pattern of equatorward movement of zones of low ecogroup specialization predominantly in the North Atlantic and North Pacific Oceans. This pattern is indicative of more complex ecological dynamics in the Northern Hemisphere compared to the Southern Hemisphere that facilitated expansion and exploitation of new ecological niches by ecogroups likely associated with northern hemisphere cryosphere development. In addition, there are region-specific responses to major climate events across oceans. Our preliminary results show that species, ecogroup, and morphogroup diversity are decoupled from each other but their changes coincide with distinctive climatic events. When testing for the relationship with environmental drivers (δ¹⁸O, δ¹³C, CO₂, and temperature) species diversity was closely correlated with temperature; ecogroup indices were correlated with oxygen isotopes; and morphogroup indices were correlated with carbon isotopes.