Distribution of dissolved and particulate 226Ra, 210Pb and 210Po in the Bismarck Sea and western equatorial Pacific Ocean

Abstract

The distribution of the radionuclides ²²⁶Ra, ²¹⁰Pb and ²¹⁰Po in the dissolved (<0.45 µm) and ²¹⁰Pb and ²¹⁰Po in the particulate (>0.45 µm) phases was measured in the upper 300 m of the Bismarck Sea off the Sepik River and along the equator from 143˚E to 152˚E in the western equatorial Pacific Ocean. ²¹⁰Pb and ²¹⁰Po occurred principally in the dissolved phase with a ²¹⁰Po/²¹⁰Pb ratio <1. Particulate matter had ²¹⁰Po/²¹⁰Pb ratios greater than 1.0. Box model calculations yielded an average atmospheric flux of ²¹⁰Pb of 4.5 mBq cm^-2 year^-1 to the ocean surface. The average residence times for dissolved ²¹⁰Po and dissolved ²¹⁰Pb were 0.27 years and 8.0 years respectively (in the mixed layer) and 1.45 years and 170 years (in the deeper layer). With an average residence time of 0.08 0.03 years, particulate ²¹⁰Po varied little between the layers. The difference in ²¹⁰Po and ²¹⁰Pb residence times reflects the greater particle reactivity of ²¹⁰Po. The flux of particulate organic carbon was calculated to be 104 21 mg m^-2 day^-1 from the upper 100 m and 180 22 mg m^-2 day^-1 from 100–300 m.