Zonal patterns of δ 13 C, δ 15 N and 210 Po in the tropical and subtropical North Pacific

Nitrogen fixation process may supply a significant fraction of bioavailable nitrogen to surface waters, increase the oceanic sequestration of atmospheric CO 2 , and alter the distribution of geochemical parameters. We report a zonal pattern of δ 15 N and δ 13 C in particulate organic matter (POM), and ratios of particulate 210 Po to dissolved 210 Po along a transect through the subtropical and tropical North Pacific. Both 15 N and 210 Po signals indicated an enhanced N 2 fixation in the northwestern subtropical North Pacific. The eastward decrease of N 2 fixation along this transect testified the role of aeolian Fe and P in controlling marine N 2 fixation. Associated with the zonal variations of 15 N and 210 Po, the δ 13 C of suspended POM increased eastward, reflecting the decrease of anthropogenic CO 2 concentration in surface seawater from west to east in the study area. Our results highlight the need to examine more closely the mechanisms of possible longitudinal variation in N 2 fixation in the ocean and the role of aeolian Fe and P in controlling marine N 2 fixation and anthropogenic CO 2 .