Disentangling the Oligocene‐Miocene transition – Extent and relationship of climate and carbon cycle variability on orbital timescales based on new geochemical record from Agulhas Plateau IODP Site U1579 (Exp. 392)

• Applicants: Eleni Anagnostou, Ph.D.; Dr. Thomas Westerhold
• Subject Area: Geology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 565936711

By the year 2100 the emission of fossil carbon to the atmosphere could shift Earth’s climate state to conditions comparable to the late Oligocene to early Miocene, that was ~23 million years ago. Much of our understanding of Earth’s past climate, in particular the interval from late Oligocene to early Miocene, comes from geochemical records generated from microfossil carbonate shells present in deep carbonate rich unconsolidated sediments retrieved by scientific ocean drilling. Very specific geochemical analysis techniques of planktic, surface dwelling, and benthic, bottom dwelling, fossil tests of unicellular organism called foraminifera can provide indirect estimates for past ambient and global temperatures as well as atmospheric CO2 concentration. Combining the geochemical proxy data allows to reconstruct polar ice mass variability as well as study the potential relation to climate and carbon cycle variability. Reliable reconstruction of these paleoenvironmental parameters require well preserved and as far as possible unaltered carbonate microfossils from unconsolidated sediment. International Ocean Discovery Program Site U1579 drilled on the Agulhas Plateau in early 2022 retrieved well preserved microfossils from ~20 meters drill depth in the sediment, a unique archive of paleoclimatic conditions. The main goal of the project is to generate geochemical records from Site U1579 sedimentary material to reconstruct key environmental parameters spanning the late Oligocene to early Miocene time (22 to 24.5 Ma) in the Southwest Indian Ocean. Well preserved carbonate tests of benthic foraminifer will be used to generate a stable carbon and oxygen isotope record that will function to establish a highly accurate astrochronology as well as document deep-ocean temperature and global polar ice sheet mass dynamics. To subsequently disentangle the temperature and ice volume components recorded in the oxygen isotope data carbonate clumped-isotope Δ47 and Mg/Ca thermometry on selected benthic foraminifer tests will be conducted. In order to reconstruct the surface ocean temperature, the same methods will be applied to planktic foraminifera tests Site U1579. Finally, boron isotope composition of planktic foraminifera will be determined to reconstruct the ambient pH of surface waters from which atmospheric pCO2 will be calculated. The resolution of samples to be analyzed will allow investigating climate variability on Milankovitch time scales of 10 to 100 thousand years. Ultimately the results will be used to test the hypothesis that eccentricity-driven cycles of 100-kyr and 405-kyr in atmospheric CO2 and sea surface temperature are closely in step with deep-sea benthic foraminifer δ18O data recording late Oligocene to early Miocene Antarctic glaciation dynamics. The project can give important new insight to the major societal relevant theme of global warming and polar ice sheet behaviour related to atmospheric CO2 concentration changes.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 527: Infrastructure area - International Ocean Drilling Programme³ (IODP³)
• International Connection: Norway
• Cooperation Partner: Professorin Dr. Anna Nele Meckler
• Co-Investigator: Dr. Heather Johnstone