Speciation Distribution of Iodine Isotopes (127I and 129I) in the North Pacific Ocean

Mr Yuanzhi Qi1, Mr. Takeyasu Yamagata1, Prof. Hisao Nagai2, Prof. Hiroyuki Matsuzaki1

1MALT, The University Of Tokyo, Tokyo, Japan, 2Nihon University, Tokyo, Japan

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. Compare to subsurface layers, surface seawater always has relative lower bulk inorganic 129I concentrations, implying some loss processes, like inorganic 129I emission and bio-utilization, exist in the surface bound layer of 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.


He is a doctoral student of Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo belonging to Matsuzaki laboratory, MALT, The University of Tokyo. He is an oceanography scientist and recently studies speciation analysis of iodine isotopes. He is a promising young scientist having skills and knowledge on field work, laboratory experiments and analytical techniques such as AMS and ICP-MS.

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Nov 17 2021


8:45 am - 9:30 am