Export and remineralization of POM in the Southern Ocean and the South China Sea estimated from 210Po/210Pb disequilibria

Abstract

Disequilibria between 210Po and 210Pb in the upper water and their potential applications as a proxy of particle export and remineralization were examined in the Southern Ocean (station IV3) and the South China Sea (NS44). 210Po was deficit in surface waters but excessive relative to 210Pb in subsurface waters. Good positive correlation between 210Po and particulate organic carbon (POC) indicated deficits and excess of 210Po resulted from particulate organic matter (POM) export and remineralization respectively, which was also supported by the decreased δ13C and increased δ15N downwards as a result of particle remineralization. On the basis of 210Po/210Pb box-model, POC export flux out of the surface waters were 1.2 mmol C · m−2 · d−1 and 2.3 mmol C · m−2 · d−1 for station NS44 and IV3, respectively. In the subsurface waters, remineralization fluxes of 210Po were 0.062 Bq · m−2 · d−1 and 0.566 Bq · m−2 · d−1 for station NS44 and IV3 along with the recycle efficiency of 52±26% and 119±52%, respectively. Remineralized fluxes of POM derived from 210Po and exported POC were 0.6 mmol C · m−2 · d−1 and 2.7 mmol C · m−2 · d−1 for NS44 and IV3. This study suggested that 210Po was a powerful tracer of particle export and remineralization.