Carbonate Burial Through The Miocene Climate Optimum: Atlantic Versus Pacific Response

The Miocene Climate Optimum (MCO; 17-13.8 Ma) is the warmest interval of the Neogene, associated with high atmospheric CO₂ and low Antarctic ice volume. This distinct perturbation in the carbon cycle implies fluctuations in marine carbonate burial. While adequate carbonate records are available in the Pacific, Miocene records for the North Atlantic are comparatively scarce. As paleoceanographic dynamics in the North Atlantic strongly influenced Cenozoic climate variability, constraining the Atlantic response to carbon cycle fluctuations is crucial for understanding the MCO.

Marine sediment cores from the Sargasso Sea between 3750 and 3800 m water depth (Sites 558 and 563; Deep Sea Drilling Project Leg 82) were analyzed using X-ray fluorescence core scanning for bulk sediment chemistry, including carbonate. These sites have well-constrained age control from bio- and magnetostratigraphy and were scanned where sediments were recovered at Milankovitch-scale resolution.

Preliminary analyses reveal low sedimentation rates and variable carbonate content across the MCO. Carbonate sedimentation in the North Atlantic significantly increases only after the Miocene Climate Transition, which ended the MCO at 13.8 Ma. In contrast, at eastern equatorial Pacific Sites U1335, U1336, and U1337, carbonate dissolution and rebound is associated with the beginning rather than the end of the MCO. This timing difference suggests independent processes in both basins.

We attribute the Atlantic carbonate signal to reduced shallow carbonate deposition and/or enhanced flux of Northern Component Water associated with increased Antarctic glaciation and heat transport. Emplacement of the main Columbia River Basalt groups (17 to 15 Ma), suggested to cause carbonate dissolution in the Pacific, does not coincide with the Atlantic carbonate changes. Basin-basin fractionation is not favored because Atlantic carbonate deposition does not increase with the Pacific carbonate decrease between 17.4 to 16.2 Ma. Atlantic and Pacific carbonate deposition appear independent of each other, suggesting that regional carbonate burial processes dominate over global processes.