Abstract The role of phytoplankton, particularly diazotrophs, in affecting in situ 210 Po scavenging has been little investigated. Here, we first report an enhanced 210 Po deficit in a cyclonic eddy core relative to its edge in the subtropical Pacific, coinciding with an elevated integrated nitrogen fixation rate (NFR). In contrast, particulate organic carbon, chlorophyll a , total particulate matter, and 210 Pb show no core‐edge difference, revealing a selective fractionation between 210 Po and 210 Pb during scavenging. The partition coefficient of 210 Po, but not 210 Pb, correlates with NFR. The 210 Po/ 210 Pb fractionation factor also scales with NFR. These relationships indicate diazotrophs' uptake of 210 Po and provide a field data‐based algorithm linking 210 Po disequilibria to NFR in (sub)tropical oceans. Our findings suggest that 210 Po offers a potential radiotracer for quantifying marine NFR, highlighting a new insight to constrain nitrogen cycling in oligotrophic oceans.
Yang et al. (Thu,) studied this question.