The effect of ocean alkalinity and carbon transfer on deep-sea carbonate ion concentration during the past five glacial cycles

Glacial-interglacial changes in deep Indian and Pacific Ocean carbonate ion concentration ([CO32−]) are mainly driven by two mechanisms that operate on different timescales: 1) a long-term increase during glaciation caused by a reduction in carbonate deposition on shelf areas (i.e, the coral reef hypothesis), and 2) transient carbonate compensation responses to changes in deep ocean carbon storage. To investigate these mechanisms, we use benthic B/Ca to reconstruct deep water [CO32-] in cores from the deep Indian and Equatorial Pacific Oceans during the past five glacial cycles.

Based on our reconstructions, we suggest that the redistribution of carbonate deposition from shelf areas to the deep ocean raised deep water [CO32−] on average by 7.3 ± 0.5 (SE) umol/kg during glaciations. Oceanic carbon reorganizations during major climatic transitions caused deep water [CO32−] deviations away from the long-term trend and carbonate compensation processes subsequently acted to restore new steady state conditions.