Impacts of the Middle Miocene Climatic Transition on deep-water carbonate preservation and oxygenation in the equatorial Indian Ocean

We reconstructed the orbital-scale variability of deep-water mass properties in the equatorial Indian Ocean during the late early to late Miocene (17.9 to 8.2 Ma) using benthic foraminiferal oxygen (delta O-18) and carbon (delta C-18) isotope records, in combination with X-ray fluorescence scanner elemental records at International Ocean Discovery Program (IODP) Site U1443. These records suggest that hyperthermal-like features (negative excursions in delta O-18 and delta C-18 coupled to suboxic and acidic conditions in the deep ocean) developed at eccentricity maxima during the Miocene Climatic Optimum (MCO; 16.9 to 14.7 Ma) on an almost ice-free Earth. Elevated Mn and U concentrations indicate that bottom and pore waters in the Indian Ocean became progressively suboxic during the later phase of the MCO. A fundamental change in deep-water circulation occurred after the expansion of the East Antarctic Ice Sheet during the Middle Miocene Climatic Transition (MMCT; 14.7 to similar to 13.8 Ma). Stepwise increases in delta O-18 at similar to 13.8 and similar to 13.1 Ma concurred with dampening of deep-water delta O-18 and delta C-18 variability, as Antarctic ice cover expanded and became more stable. A marked improvement in deep-water oxygenation after similar to 13.5 Ma coincided with the end of the last delta C-18 maximum of the Monterey Excursion. Carbonate dissolution in the equatorial Indian Ocean intensified and prolonged episodes of reduced carbonate deposition during the Carbonate Crash interval (similar to 12.6 to 8.6 Ma) were not restricted to eccentricity maxima as during the MCO. Rising Mn and U concentrations after similar to 9 Ma indicate decreased oxygenation of bottom and pore waters, associated with the onset of the Biogenic Bloom in the Indian Ocean.

Automated summary

By reconstructing orbital-scale variability of deep-water mass properties in the equatorial Indian Ocean during the late early to late Miocene, it was found that hyperthermal-like features occurred during the Miocene Climatic Optimum, and a fundamental change in deep-water circulation occurred after the Middle Miocene Climatic Transition.