The carbonate compensation depth (CCD), defined as the depth in the ocean where the supply rate of pelagic carbonate is balanced by its dissolution, provides an important parameter for estimating the amount of calcium carbonate-bound carbon that is stored in deep-sea sediments. The CCD is reasonably well-constrained across the Atlantic and Pacific oceans; however, our understanding of the regional CCD evolution across the Indian Ocean is limited to very broad relationships and a tightly confined region of the western equatorial sector. Here, we reconstruct the evolution of the CCD since the late Oligocene in three key regions of the Indian Ocean: the western equatorial Indian Ocean, the southeast Indian Ocean, and the Southern Ocean. We find that the CCD shows region-specific fluctuations of ~ 1–1.5 km over the last 15 Ma, marked by a long-term deepening pattern from ~ 3.5 km in the late Oligocene to ~ 4.4 km in the Pliocene across the western equatorial region, which was at its shallowest (~ 3.6 km) by ~ 27.5 Ma, and at its deepest (~ 4.4 km) by ~ 7.5–7 and ~ 4.5 Ma. In comparison, the southeast Indian and Southern oceans maintained relatively shallower CCDs, fluctuating between ~ 2.7 and 3.5 km and 3.4 and 4 km, respectively, since the late Miocene, consistent with the latitudinal gradient in carbonate flux and seafloor bathymetry. We propose that CCD variability across the equatorial Indian Ocean is driven by atmospheric CO2 fluctuations, the dynamics of the Tethyan and Indonesian seaways, and the development of the Indo-Pacific water exchange since the late Oligocene. Peaks in carbonate productivity align with the establishment of the Pacific warm pool and the intensification of the Indian monsoons since the middle Miocene, with peak intensity contributing to the biogenic bloom interval of the late Miocene. The new regional CCD models provide a foundation for estimating the evolution of deep-sea carbonate carbon reservoirs across the Indian Ocean within the framework of the long-term global carbon cycle.
Dalvand, F., Dutkiewicz, A., Wright, N.M., Müller, R.D., 2025, Indian Ocean carbonate compensation depth since the Late Oligocene. Geo-Mar Lett 45, 38. https://doi.org/10.1007/s00367-025-00825-5
