Anomalous >2000 year old surface ocean radiocarbon age as evidence for deglacial geologic carbon release

Geologic carbon from seafloor volcanism may influence late-Pleistocene glacial terminations by increasing the global inventory of the greenhouse gas CO₂. However, the evidence for geologic carbon flux associated with deep-sea volcanism has been, so far, equivocal. Here, we construct a regional, glacial-interglacial carbon budget of the volcanically-active Gulf of California using microfossil ¹⁴C reconstructions and find results consistent with an increased addition of geologic carbon related to local seafloor volcanism during the deglaciation. Our estimates point to enhanced geologic carbon flux both before and during the last deglaciation that generally occur alongside carbonate preservation. This leads us to suggest that the carbon was added in the form of partially neutralized, ¹⁴C-free bicarbonate associated with associated with sill emplacement and enhanced anaerobic oxidation of thermogenic hydrocarbons —a carbon source that would have a limited affect on atmospheric CO₂.