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

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. Supported by National Natural Science Foundation of China (Grant Nos. 40576037 and 90411016), National Key Technology Research and Development Program (Grant No. 2006BAB19B03) and COMRA project (Grant No. DYXM-115-01-3-04)