Radiocarbon ages of western Pacific intermediate waters during the past 25 kyrs: Implications for global carbon cycling

The rapid increase of atmospheric carbon dioxide (CO₂) and the concurrent decline in Δ¹⁴C during the last deglaciation were mainly ascribed to the release of old, ¹⁴C-depleted CO₂ from an abyssal ocean reservoir, specifically the Southern Ocean, or the deep Pacific Ocean via intermediate waters. In support of this hypothesis, several records from intermediate waters around the globe depict a drop in Δ¹⁴C during the deglaciation. However, other records closer to the source regions of intermediate waters do not depict this anomaly and thus, question the hypothesis. Alternative scenarios include the release of ¹⁴C-depleted CO₂ by hydrothermal vents, volcanoes and pockmarks. An ideal region to test the hypothesized scenarios is the western equatorial Pacific Ocean (WEP), where intermediate waters of southern and northern origin converge.

We present paired planktic and benthic foraminiferal ¹⁴C ages from a depth transect (404 – 2210 m) of seven gravity cores from the WEP that cover the past 25 kyrs. Our records do not show any discernible Δ¹⁴C anomaly during the Last Glacial Maximum and initial deglaciation making the WEP an unlikely candidate for the release and ventilation of oceanic CO₂ to the atmosphere. However, the intermediate-depth records consistently show anomalously low benthic Δ¹⁴C values during the final stage of the deglaciation and early Holocene. This Δ¹⁴C variability will be discussed in the context of potential sources and mechanisms.