Helium isotopes of seawater in the Philippine Sea and the western North Pacific

We measured helium isotopic ratios of 84 seawater samples from various depths collected in the western North Pacific Ocean and the western Philippine Sea The He-3/He-4 ratios varied significantly from delta He-3 of 0 1% to 22 9% where delta He-3 is defined as the percent deviation of the helium isotopic ratio relative to the atmospheric standard Maximum (delta He-3 > 20% was observed at mid depth (2000-2500 m) in the western Philippine Sea and in the southern part (similar to 10 degrees N) of the western North Pacific, though not in the northern part (similar to 30 degrees N) at the same depth Contour maps of the lateral delta He-3 distribution at mid depth suggest that the helium 3 plume derived from the East Pacific Rise does not flow northward along the Izu-Ogasawara-Mariana Ridge but westward through the Caroline Basin or the Yap-Mariana Junction into the Philippine Sea It then flows northward in the western Philippine Sea to a region adjacent to the Japanese Islands Although these flows inferred from the delta He-3 distribution are roughly similar to those estimated from water properties such as isopycnal distributions, the delta He-3 distribution could reveal that deep water circulation seems to be different at each depth (2000 2500, 3000 m)