A Global View of Deep Ocean Carbonate Ion Concentration Over Glacial-Interglacial Cycles and the Effects on Atmospheric pCO2
Abstract:Deep ocean carbonate chemistry is inherently linked to atmospheric CO2 concentration, a fundamental driver of glacial-interglacial climate change. Deep ocean carbonate ion concentration ([CO32-]), carbon isotope ratio (δ13C), and sediment CaCO3% impose crucial constraints on the carbonate system throughout glacial cycles, providing important indicators of why atmospheric pCO2 shifted between strict upper and lower bounds. We present the first medium to high resolution deep ocean [CO32-] records that span more than one full glacial cycle, extending to MIS 12, in a number of key locations such as the South Atlantic, Central Pacific, and Indian Oceans. In the South Atlantic Ocean, at 3702m, our results show unprecedented glacial-interglacial [CO32-] increases of 40-50 μmol/kg that are preceded by a positive shift in δ13C. Coupled with deglacial [CO32-] peaks in the Pacific and Indian Oceans, and a steady decrease in South Atlantic [CO32-] and δ13C during glaciations, our results strongly support suggestions that atmospheric CO2 was stored in the stratified glacial deep ocean and released during reinvigoration of ocean circulation.
The ocean circulation driven response of deep South Atlantic [CO32-] is reproducible over successive glacial cycles, however this is not replicated in the Pacific Ocean. Deep Equatorial Pacific [CO32-] gradually increased by 25 μmol/kg throughout glaciation from MIS 5 - MIS 2. However, during the MIS 7 - MIS 6 transition, [CO32-] increased by 15 μmol/kg in less than 20Kyr and remained unchanged during a further ~80Kyr of atmospheric pCO2 decline. This highlights the requirement for long term [CO32-] records to fully constrain carbonate system influences on atmospheric pCO2. Even a small rise in Deep Pacific Ocean [CO32-] could increase glacial CO2 storage further than changes in ocean circulation alone.