Evidence for Increased Reservoir Ages and Poorly Ventilated Deep Waters in the Glacial Eastern Equatorial Pacific

It has been hypothesised that a poorly ventilated deep Pacific Ocean would have contributed significantly to reduce glacial atmospheric CO2. Although radiocarbon evidence for a deglacial rise in deep Pacific ventilation so far remains conflicting, this may stem in part from surface reservoir age uncertainties and their effect on inferred deep ocean ventilation ages. Here we use chronostratigraphic calendar age constraints to estimate surface reservoir age variability, and therefore deep ventilation ages, in the Eastern Equatorial Pacific over the last 25 kyr. Both the shallow- and deep ventilation records show a deglacial decrease in glacial radiocarbon depletion, consistent with other South Pacific and Southern Ocean ventilation reconstructions where surface reservoir ages have been assessed. We propose that this basin-wide agreement can be explained by ocean interior transport pathways similar to the modern, implying significantly reduced air-sea gas exchange in the southern high latitudes during the last glacial period.