ASSESSING THE IMPACTS OF OCEAN ACIDIFICATION AND WARMING ON FORAMINIFERAL TEST SIZE AND PRESERVATION: INSIGHTS FROM THE PALEOCENE-EOCENE THERMAL MAXIMUM RECORD AT OCEAN DRILLING PROGRAM SITE 1266 (WALVIS RIDGE)

Investigation of deep-sea sediments can offer rich insight into past climate and oceanographic conditions, with records preserving periods of abrupt climate change serving as ancient analogs for predicting future climate fluctuations. One significant event that has been identified as an ancient analog for modern climate change is the Paleocene-Eocene Thermal Maximum (PETM). During the PETM the oceans experienced acidification, expanded deoxygenation, and increased temperatures in the sea surface and deep ocean. In this study we evaluate the preservation of foraminifera tests by assessing the proportion of broken, whole, and fragmented tests throughout the deep sea PETM record of Ocean Drilling Program Site 1266C (Walvis Ridge, southeast Atlantic Ocean). To understand the biological response of foraminifera during this period, this research also investigates changes in the test size of foraminifera that inhabit different marine environments, including planktic foraminifera living in the mixed layer (i.e., Acarinina, Morozovella) and thermocline (i.e., Subbotina, Chiloguembelina) as well as benthic foraminifera. Decreases in the weight % CaCO₃ and fraction of coarse sediments, and increases in shell fragmentation at Site 1266C indicate increased dissolution during the PETM caused by ocean acidification. Preliminary results also show that the average size of planktic foraminiferal tests increased during the PETM, with different degrees of shell-size change among mixed-layer versus thermocline-dwelling taxa, whereas benthic foraminiferal test size decreased. Shell sizes returned to or fell below pre-PETM levels during the recovery period post-PETM. These results can serve as a model for understanding the effects of ocean acidification and warming on foraminifera living in our modern ocean.