[10p-N402-1~10] CS.1 Code-sharing Session of 2.3 & 7.5

▼ [10p-N402-9] Speciation Distribution of Iodine Isotopes (¹²⁷I and ¹²⁹I) in the North Pacific Ocean

〇(D)Yuanzhi Qi¹, Hiroyuki Matsuzaki¹ (1.The Univ. of Tokyo)

Keywords:iodine-129, speciation analysis, seawater

Bulk inorganic ¹²⁷I and ¹²⁹I, as well as for iodide and iodate of these two isotopes, were measured in seawater of different depth profiles in the north Pacific Ocean. The bulk inorganic ¹²⁹I concentrations were 1.16 ~ 1.71 × 10⁷ atoms L^-1 in surface waters, and the vertical profiles almost have same trend, which is that the ¹²⁹I concentration decrease with depth from the subsurface layer, among all study stations. The same trend indicates that atmospheric deposition may be the overwhelming ¹²⁹I source in the North Pacific Ocean. Based on the measured bulk ¹²⁹I concentrations, the ¹²⁹I inventories in the upper layer (to the depth of 800 m) of North Pacific Ocean are 5.0 ~ 9.1 × 10¹¹ atoms m⁻². As the thermodynamically stable form of iodine in normal seawater, iodate is the predominant ¹²⁷I species (35.8 ~ 63.7 µg/L, accounting for 72.6 ~ 97.5% of bulk ¹²⁷I) in the North Pacific Ocean. However, the ¹²⁹I/¹²⁷I ratio in iodide is much higher than which in iodate, indicating that ¹²⁷I and ¹²⁹I have different circulation pathway. Besides, due to the exist of eastern subtropical North Pacific oxygen minimum zones (ESTNP-OMZs), the ¹²⁷I^--¹²⁷IO₃^- differences in the eastern Pacific Ocean are obvious less in comparison with which in the western Pacific Ocean, at the same time, the differences between ¹²⁹I^-/¹²⁷I^- and ¹²⁹IO₃^-/¹²⁷IO₃^- also decrease in the eastern Pacific Ocean. The results suggest that in-situ reduction from iodate to iodide occurs in the ESTNP-OMZs.