Obliquity Pacing of Deep Pacific Carbonate Chemistry During the Plio‐Pleistocene

Reconstruction of the seawater carbonate system is essential for an improved understanding of glacial-interglacial oceanic carbon cycling and climate change. However, continuous high-resolution ocean carbonate chemistry data are generally lacking for the Plio-Pleistocene. Here, we present a deep Pacific carbonate ion saturation state (Δ[CO32−]) record spanning the last 5.1 Myr, reconstructed from the size-normalized shell weight of planktonic foraminifer in the western tropical Pacific. Deep Pacific Δ[CO32−] has been modulated primarily by orbital obliquity since 5.1 Ma, during which it has exhibited in-phase behavior with the 40-Kyr obliquity cycle. Significantly, the amplitude of the 40-Kyr Δ[CO32−] cycles has responded linearly to obliquity forcing throughout the Plio-Pleistocene, independent of the late Pliocene intensification of Northern Hemisphere glaciation. We speculate that the obliquity signal in the deep Pacific Δ[CO32−] record reflects an ocean-atmosphere circulation feedback mediated by migration of the Southern Hemisphere Westerlies. Key Points: - Deep Pacific Δ[CO32−] has been modulated primarily by orbital obliquity since 5.1 Ma - 40-Kyr Δ[CO32−] cycles were in-phase with and responded linearly to 40-Kyr band obliquity forcing - Plio-Pleistocene glacial cycles of deep Pacific carbon storage were linked to meridional migration of the Southern Hemisphere Westerlies