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

<p>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.</p><p>Global &#948;18O 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 4&#186;C range with near-freezing temperatures occurring at every glacial maximum, especially after the Mid-Pleistocene transition [2,3]. However, temperature signals based on carbonate &#948;18O data are built upon uncertain assumptions of non-thermal factors such as those regarding the isotopic composition of the ancient seawater.</p><p>Carbonate clumped thermometry (&#120549;47) is based on thermodynamic principles that determine the ordering of isotopes within the carbonate crystal lattice [4]. It is independent of the fluid composition. &#120549;47 thermometry has recently been used to anchor Mg/Ca records of the Miocene while revealing a comparatively warm deep ocean [5].</p><p>Here we present &#120549;47-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 &#948;18O 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.</p><p>[1] Zachos, J., et al. (2001), Science 292, 686-693.</p><p>[2] Westerhold, T., et al. (2020), Science, 369, 1383&#8211;1387,</p><p>[3] Elderfield, H., et al. (2012) Science, 337(6095), 704-709.</p><p>[4] Eiler, J.M. (2007), Earth Planet. Sci. Lett. 262, 309-327.</p><p>[5] Modestou, S. E., et al. (2020) Paleoceanography and Paleoclimatology 35, e2020PA003927.</p>