the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Oct 2026
Regional low-latitude planktic δ18O and Mg/Ca proxy response to changes in middle Miocene global ocean overturning circulation
Abstract. Palaeoceanographic records suggest that a reorganization of low-latitude ocean-atmosphere dynamics occurred across the Middle Miocene Climate Transition (MMCT, 14.7-13.8 million years ago), but the mechanisms connecting global climate forcing to regional patterns are yet uncertain. The current paradigm for explaining this transition is tied to increasing latitudinal temperature gradients forced by global climate cooling due to decreasing atmospheric CO₂ concentrations. One overlooked possibility is the impact of changes in global ocean circulation patterns. Here, we use mid-Miocene simulations with an isotope-enabled model to investigate the fingerprint of global ocean circulation versus CO2 levels on regional temperature, salinity, and the oxygen isotopic composition (δ¹⁸O) of seawater. We then explore how these parameters would be encoded in multi- and individual-test planktic foraminiferal δ¹⁸O and Mg/Ca analyses using a proxy system model. Our results show that seawater δ18O, as opposed to temperature reconstructions, has the potential to delineate regional changes driven by perturbations to global ocean circulation. These predictions help evaluate where and how effectively tropical records inform us about the relative contributions of CO2 forcing versus ocean circulation changes in driving the MMCT and other climate transitions across the Miocene.
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Status: open (until 17 Dec 2026)
- CC1: 'Comment on egusphere-2026-6271', Giacomo Medici, 27 Oct 2026 reply
Data sets
Code for Figures, Simulations and Proxy System Model outputs for iCESM1.2 Miocene simulations with multiple Meridional Overturning Circulation states (v2) Sarr, A-C., Thirumalai, K., Lee, D., Acosta, R.P. https://doi.org/10.5281/zenodo.23216768
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General comments
Very good research on paleoclimate with global angle. Please, consider the specific comments to improve the final version.
Specific comments
Lines 23-89. Highlight much better the existing novelty of your research.
Lines 23-26. Insert recent literature on interactions between marine carbon cycling, high-latitude ice extent, and ocean-atmospheric dynamics with use of stable isotopes (e.g., δ18O):
- 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), 17.
- Hu, Y., Liu, Z., Zhang, Y., He, H., Yan, H., Zhao, M., Bao, Q., Zeng, C., Wang, D., Zhang, Y. and Guo, Q., 2025. Land cover influences on Asian summer monsoon δ18O signals in groundwater: Implications for paleoclimate interpretation. Journal of Hydrology, 134241.
Line 89. Describe the three to four specific objectives of your research by using numbers (e.g., i, ii, and iii).
Line 96. If you run simulations setting-up a numerical model you should validate your outputs. Make this point clearer in the methodology and discussion sections.
Lines 600-614. Highlight much better the existing novelty of your research also for this section.
Line 625. The word “validated” appears only in an appendix. You should make clear how the outputs from figures 1 to 8 are validated.
Figures and tables
Figure 6. Difficult to read numbers on the axes and equations. Please, improve.
Figure 6. The description in the caption is too long. Consider moving some of this information in the result section.
Figures 1, 2, 3, 4, 5, 7 and 8. Some details are difficult to read on the maps. There is room to enlarge the maps.
Figures 1, 2, 3, 4, 5, 7 and 8. Enlarge the font size for numbers and letters.
Figures 1, 2, 3, 4, 5, 7 and 8. Increase the number of DPI of the figures if possible.
Table 1. Provide more information in the caption.