| 12 Aug 2026
Quantifying trends and transitions in a Miocene benthic δ18O stack
Abstract. Marine isotopic records from benthic foraminifera are central to understanding Miocene climate, but developing reliable Miocene age models that are consistent across sites has been challenging due ambiguities in biostratigraphy and magnetostratigraphy. Detailed chemostratigraphic alignment of globally distributed marine records can assist in comparing paleoclimate proxy records and their proposed forcing mechanisms. We present a continuous benthic δ18O stack (average) across the Miocene based on alignment of published records from 24 sites. Stack estimates of global mean benthic δ18O changes may improve reconstructions of Miocene ice volume change and deep-sea cooling and help distinguish between causal mechanisms. We estimate the rate of change in the global stack’s benthic δ18O throughout the Miocene as well as the amplitude of abrupt transitions associated with the onset of the Miocene Climatic Optimum (MCO) and the Middle Miocene Climatic Transition (MMCT). We find that the global stack’s change in benthic δ18O across the abrupt onset of the MCO at ~16.9 Ma is 0.27 ‰, which is about half the amplitude recorded in the deep Eastern Equatorial Pacific (EEP) and in the CENOGRID splice (Westerhold et al., 2020). We additionally find the total change in stack benthic δ18O across the Miocene is 0.82 ‰, which is 15 % less than in the CENOGRID splice.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Climate of the Past.
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General comments
Very good research on paleoclimate. Please, follow my suggestion to improve the manuscript.
Specific comments
Lines 21-39. The introduction is very short. You need to expand starting more general.
Line 21. Insert a general introduction on oxygen isotope ratio δ18O to study the paleoclimate of the overall Cenozoic period referring to recent literature, see below:
- Rohling, E. J., T. M. Gernon, D. Heslop, G. J. Reichart, A. P. Roberts, J. Yu 2024. Reconciling the apparent discrepancy between Cenozoic deep‐sea temperatures from proxies and from benthic oxygen isotope deconvolution. Paleoceanography and Paleoclimatology 39, 11, e2024PA004872.
- Medici, G., Marianelli, D., Cornacchia, I., Gori, F. Brandano, M. 2026. Multi-disciplinary approach to paleokarst occurrence in the Eocene–Oligocene succession of the Apulia Carbonate Platform (Salento, Italy). Facies, 72(2).
- Mudelsee, Manfred, Torsten Bickert, Caroline H. Lear, Gerrit Lohmann 2014. Cenozoic climate changes: A review based on time series analysis of marine benthic δ18O records. Reviews of Geophysics 52, 333-374.
Line 39. Disclose the specific objectives of your research by using numbers (e.g., i, ii, and iii)
Lines 46-84. You should mention somewhere in the manuscript the importance of orogenesis (e.g., Alps, Pyrenees, Himalaya) on oxygen isotope ratio δ18O in the stratigraphic record.
Line 57. I agree on the importance of the volcanism in your manuscript, and I have studied the Columbia Plateau between Washington and Idaho! However, the Miocene was affected by intense volcanisim also in other areas of the world (e.g., Mediterranean region) due to the subduction zones. Can the activities from other volcanic districts be relevant to your research?
Lines 311-324. Highlight better the potential large impact of your research. The Conclusion section is very short.
Figures and tables
Figure 1. There is the chance to increase the graphic resolution as well as enlarge the figure.
Figure 2. Increase the font size for the axes.
Figure 3. Explain the meaning of the vertical and coloured bands in the caption.
Figure 6. Do you need to insert formal internal boundaries for the Miocene age on this figure?
Figure 6. Key figure of large impact. Please, pay attention to the graphic resolution and the information in the caption.