South Atlantic deep-sea temperature evolution across the Pliocene-Pleistocene transition from clumped isotope thermometry

The reconstruction of deep-ocean temperatures is key in the study of the different climate states in the geological past. Reconstructions covering the Pliocene-Pleistocene transition shed light on the global climatic change that followed the mid-Pliocene warm period and culminated in full glaciation of the Northern Hemisphere.

Global δ18O records measured on seafloor dwelling foraminifera constitute the backbone of our understanding of the climatic trends and transitions of the last 65 million years [1,2]. These records suggest that the glacial intensification over the last 2.8 Ma experienced the onset of Quaternary-style ice age cycles and the progression towards a more deterministic climate system increasingly sensitive to orbital forcings. Deep-sea temperature variability across this time is thought to have stayed in a 4ºC range with near-freezing temperatures occurring at every glacial maximum, especially after the Mid-Pleistocene transition [2,3]. However, temperature signals based on carbonate δ18O data are built upon uncertain assumptions of non-thermal factors such as those regarding the isotopic composition of the ancient seawater.

Carbonate clumped thermometry (𝛥47) is based on thermodynamic principles that determine the ordering of isotopes within the carbonate crystal lattice [4]. It is independent of the fluid composition. 𝛥47 thermometry has recently been used to anchor Mg/Ca records of the Miocene while revealing a comparatively warm deep ocean [5].

Here we present 𝛥47-based deep-sea temperature constraints across the Pliocene-Pleistocene transition obtained from benthic foraminifera of ODP Site 1264 in the South Atlantic Ocean. In combination with benthic δ18O analyses, we furthermore interpret our measurements into global ice volume and ocean circulation changes in the Atlantic Basin across the major onset of the Northern Hemisphere Glaciation.

[1] Zachos, J., et al. (2001), Science 292, 686-693.

[2] Westerhold, T., et al. (2020), Science, 369, 1383–1387,

[3] Elderfield, H., et al. (2012) Science, 337(6095), 704-709.

[4] Eiler, J.M. (2007), Earth Planet. Sci. Lett. 262, 309-327.

[5] Modestou, S. E., et al. (2020) Paleoceanography and Paleoclimatology 35, e2020PA003927.