Time-series observation of ²¹⁰Pb sinking fluxes in the western North Pacific

We observed the lead-210 (²¹⁰Pb) sinking flux in subarctic and subtropical regions of the western North Pacific Ocean over time. The ²¹⁰Pb fluxes in the mesopelagic and bathypelagic zones were estimated from the disequilibrium between ²¹⁰Pb and radium-226 (²²⁶Ra) in the water column over the 4 seasons during several years. In the subarctic region, ²¹⁰Pb fluxes were larger (28–29 dpm m^–2 d^–1 at 500 m; 68–70 dpm m^–2 d^–1 at 4810 m) than those in the subtropical region (22–24 dpm m^–2 d^–1 at 500 m; 46–49 dpm m^–2 d^–1 at 4810 m). These results imply that the strength of the biological pump in the mesopelagic and bathypelagic zones is larger in the subarctic region than in the subtropical region of the western North Pacific. We also determined ²¹⁰Pb in sinking particles collected by moored sediment traps. In the subarctic (subtropical) region, the annual average of trapped ²¹⁰Pb flux at 500 and 4810 m were 3.0 (4.6) and 24.2 (18.6) dpm m^–2 d^–1, respectively. Estimated from the ²¹⁰Pb flux in the water column and the ²¹⁰Pb flux in the sinking particles in the sediment trap experiment, the trapping efficiencies at 500 m (10–20%) were about a half of those at 4810 m (35–40%) in the sediment trap experiment.