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.