Shortcomings of the isolated abyssal reservoir model for deglacial radiocarbon changes in the mid-depth Indo-Pacific Ocean

Severely negative ¹⁴C anomalies from the mid-depth Pacific and the Arabian Sea have been taken as support for the hypothesized deglacial release of a previously isolated, extremely ¹⁴C-deplete deep ocean carbon reservoir. We report box model simulations that cast doubt on both the existence of the hypothesized deep reservoir and its ability to explain the mid-depth ¹⁴C anomalies. First, the degree of ice age isolation needed to substantially reduce the deep ¹⁴C of the deep reservoir causes anoxia and the trapping of alkalinity from CaCO₃ dissolution, the latter increasing atmospheric CO₂. Second, even with a completely ¹⁴C-free deep reservoir, achieving the mid-depth ¹⁴C anomalies of observed duration requires ad hoc stifling of aspects of deep circulation to prevent rapid dissipation of the anomalous ¹⁴C-free carbon to the rest of the ocean and the atmosphere. We suggest that the mid-depth anomalies do not record basin-scale ¹⁴C changes but are instead local phenomena.