Spatial and Temporal Variability of Eastern Pacific Radiocarbon and Carbon Chemistry From the Ice Age to Today

Abstract Proxy records of seawater radiocarbon ( 14 C/C) provide strong constraints on how changes in ocean ventilation contributed to the increase in atmospheric CO 2 during the termination of the last ice age (≈18,000‐to‐12,000 years ago). One outstanding problem, however, is the existence of anomalously low deglacial benthic foraminiferal 14 C/C in the intermediate‐depth Eastern Tropical North Pacific (ETNP) near the Gulf of California (GoC). This deglacial ETNP 14 C/C anomaly is hypothesized to reflect either (a) an artifact of the proxy record, (b) the advection of low 14 C/C seawater, or (c) the input of 14 C/C‐depleted geologic carbon related to local seafloor volcanism. To test these hypotheses, we first use new sediment‐trap and seaweed 14 C/C to establish a new baseline understanding of ETNP seawater 14 C/C, which suggest that anomalously low 14 C/C is upwelled in the modern GoC. We then apply new geochemical experiments to test and ultimately validate the utility of the benthic foraminiferal 14 C/C as a proxy for seawater 14 C/C. Finally, we present a compilation of published and new glacial‐interglacial benthic foraminiferal 14 C/C records, specifically developed to map the spatial and temporal variability of the intermediate‐depth water mass containing the deglacial ETNP 14 C/C anomaly. These results clearly show that the ETNP deglacial 14 C/C anomaly develops near the GoC mouth, concomitant with local hydrothermal systems. Considering these results and those of our companion paper (Green et al., 2026, https://doi.org/10.1029/2025pa005217 ), we argue that the input of pH‐neutral geologic carbon from hydrothermal vents near and within the GoC could explain the anomalous intermediate‐depth 14 C/C values both during the deglaciation and today.