Deep Pacific carbonate chemistry since the Last Glacial Maximum

Quantitative constraints on deep ocean carbonate chemistry are critical for understanding the processes responsible for glacial-interglacial changes in atmospheric p CO 2 and the ocean feedbacks that amplify carbon cycle change. Here, we present a new, high-resolution, B/Ca-based record of carbonate ion concentration (Δ[CO 3 2− ]) from central equatorial Pacific site ML1208-16BB spanning the last 35 kyr. This site, bathed by Pacific Deep Water, reveals a ∼24 ± 7 μmol/kg rise in deep ocean [CO 3 2− ] between ∼20 and 10 kyr, a larger change than previously reconstructed from sites in the western equatorial Pacific and those in the central equatorial Pacific bathed by Lower Circumpolar Deep Water. Our new reconstruction permits estimation of deep Pacific calcite saturation state (Ω), quantifying the degree of deep water undersaturation during the Last Glacial Maximum and implying a critical role for sedimentary porewater saturation state in resolving the Pacific carbonate preservation paradox. Finally, we pair our Δ[CO 3 2− ] reconstruction with previously-published benthic δ 13 C to present a process-oriented understanding of late glacial, deglacial, and Holocene deep Pacific carbonate chemistry changes. Our data suggest a larger role for glacial and deglacial alkalinity changes than previously suggested by records from the equatorial Pacific Ocean.