Radiocarbon age anomaly at intermediate water depth in the Pacific Ocean during the last deglaciation

Benthic and planktonic C-14 ages are presented for the last glacial termination from marine sediment core VM21-30 from 617 m in the eastern equatorial Pacific. The benthic-planktonic C-14 age differences in the core increased to more than 6000 years between Heinrich 1 time and the end of the Younger Dryas period. Several replicated C-14 ages on different benthic and planktonic species from the same samples within the deglacial section of the core indicate a minimal amount of bioturbation. Scanning electron microscopy reveals no evidence of calcite alteration or contamination. The oxygen isotope stratigraphy of planktonic and benthic foraminifera does not indicate anomalously old (glacial age) values, and there is no evidence of a large negative stable carbon isotope excursion in benthic foraminifera that would indicate input of old carbon from dissociated methane. It appears, therefore, that the benthic C-14 excursion in this core is not an artifact of diagenesis, bioturbation, or a pulse of methane. A benthic Delta C-14 stratigraphy reconstructed from the C-14 ages from the deglacial section of VM21-30 appears to match that of Baja margin core MV99-MC19/GC31/PC08 (705 m), but the magnitude of the low-C-14 excursion is much larger in the VM21-30 record. This would seem to imply that the VM21-30 core was closer to the source of C-14-depleted waters during the deglaciation, but the source of this CO2 remains elusive.