ENVIRONMENTAL DRIVERS OF BIOGEOGRAPHIC RANGE WITHIN PLANKTONIC FORAMINIFERA DURING THE PIACENZIAN, PLIOCENE

Climate change poses an imminent threat to the future of ecosystems on land and in the oceans. Deciphering ecological patterns and environmental drivers across ancient climatic perturbations enhances our understanding of extinction risk associated with an increase in global mean temperature during the next century. This study investigates biogeographic ranges of 19 extant species of planktonic foraminifera across the Piacenzian Age(~3.6–2.6 Ma).The planktonic foraminifera exhibit the most complete species-level fossil record of any known phylogenetic group. Their global distributions, and readily preserved calcareous skeletons which record a biogeochemical fingerprint of seawater chemistry, signify the single greatest archive known to science for understanding ancient patterns in paleoceanography, biogeography, and evolution. We apply this incomparable biological record to the Piacenzian and investigate the relationship with environmental variables such as δ18O, δ13C, temperature, and CO₂.

We subset species occurrences and climate parameters into ten 100 kyr time bins to determine the relationship between biogeographic range and global climatic conditions, which was tested using a generalized least squares regression (GLS) model. Furthermore, all species were assigned to their documented morphological and ecological functional groups to assess the relationship between climate dynamics and ecological niche.

Based on the results of GLS modeling, 12 species show the strongest correlation with δ18O and temperature, 5 species show the strongest correlation with δ18O and δ13C, and 2 species show the strongest correlation with δ18O, δ13C, and temperature. Ocean temperatures are the greatest driver for planktonic foraminiferal diversity in the modern ocean, and our results suggest that many extant species which existed during the Piacenzian responded in tandem with global changes in ocean temperature and ice volume. Our results show that foraminiferal ranges contracted and shifted towards higher latitudes across the mid-Pliocene Warm Period, and we predict that similar habitat changes may be expected as anthropogenic forcing continues driving the Earth towards Pliocene-like levels of warmth, and beyond