Loss of respired carbon from the South Pacific during the last glacial termination

The last glacial termination featured a 80-ppm rise in atmospheric CO₂. This rise, which occurred in two major pulses, has been attributed primarily to release of respired carbon from the deep ocean, but the specific source(s) and release mechanism(s) of this CO₂ have not been fully resolved. Here we present a three-core depth transect of benthic B/Ca-derived paleo carbonate ion concentrations ([CO₃^2-]) from off of northern New Zealand, at the outer fringe of the Southern Ocean. When paired with carbon isotope data, B/Ca in Cibicidoides wuellerstorfi provide evidence for enrichment of respired CO₂ between 1,600 and 2,500 m water depth during the Last Glacial Maximum. Beginning 18,000 yrs ago, our records indicate pulsed changes in this deeply sequestered respired CO₂. The first major rise in atmospheric CO₂ during the last deglaciation, at the time of Heinrich Stadial 1, was accompanied by a decline in respired carbon at 1,100 m water depth. We attribute this initial pulse to an increase in wind-driven vertical mixing in the Southern Ocean. Respired CO₂ was subsequently lost from deeper depths at 1,600 and 2,500 m. Our results confirm that Southern Pacific interior water masses served as an important reservoir for CO₂ during the last glacial cycle.