Onset of ‘Pacific-style’ deep-sea sedimentary carbonate cycles at the mid-Pleistocene transition

The calcium carbonate (CaCO3) content of deep-sea sediments in the Pacific Ocean increases during glacials of the late Pleistocene in comparison to interglacials, whereas records of sedimentary CaCO3 in the Atlantic Ocean show an anticorrelated pattern across glacial-interglacial cycles. Here we show that this anticorrelation in inter-ocean CaCO3 cycles arose comparatively recently, at ~ 1.10 million years ago (Ma), during the mid-Pleistocene transition. Before this time, we show that the CaCO3 content of Pacific and Atlantic Ocean sediments experienced in-phase cyclicity, both having ‘Atlantic-style’ phasing with respect to glacial–interglacial cycles. The onset of anticorrelated cyclicity at 1.10 Ma involved a twofold switch in the Pacific's CaCO3 cycles: glacial CaCO3 preservation became consistently better while interglacial preservation became consistently worse. We demonstrate that the cause of this glacial–interglacial ‘mirror imaging’ of Pacific CaCO3 dissolution cyclicity at 1.10 Ma was a switching over of the relative ventilation state of abyssal South Pacific waters between glacials and interglacials. Specifically, we suggest that a consistent strengthening of deep water ventilation within the Pacific sector of the Southern Ocean during glacials drove glacial Pacific CaCO3 dissolution to diminish, while a contemporaneous weakening of very well-ventilated ‘upstream’ North Atlantic Deep Water during interglacials drove interglacial Pacific CaCO3 dissolution ‘downstream’ to intensify. We propose that the increased mean alkalinity of the global deep ocean (driven by the geographically and bathymetrically vast Pacific Ocean) during glacials after 1.10 Ma may explain part of the drawdown in glacial atmospheric CO2 levels hypothesised to have been linked to the increased severity of these late Pleistocene glacials.

► Pre-1.1 Myr ago, Atlantic & Pacific glacial–interglacial CaCO3 cycles were in-phase.
► Onset of ‘Pacific-style’ CaCO3 cycles occurred comparatively recently — 1.1 Myr ago.
► Onset caused by strengthened glacial-age Southern Ocean Pacific sector overturning.
► Elevated alkalinity of glacial Pacific post-1.1 Ma may have lowered glacial pCO2.