Iodine (I)

Atomic number: 53
Atomic weight: 126.9045
Average concentration in ocean: 460 nmol/kg
Residence time: 340,000 yearrs

The iodate ion (IO3-) is the stable form of iodine in seawater.  However, in the euphotic zone, some of IO3- is reduced to I- as phytoplankton reduce NO3- to NO2-

Distribution in ocean
The vertical profile of IO3- is slightly depleted at the surface due to uptake and removal, while the I- concentation has a surface maximum (data).

Residence time
The iodine residence time is from Tracers in the Sea (Broecker, W. S. and Peng, T.-H., 1982.  Eldigo Press, Palisades, NY).  It was calculated from the global average river input.

Iodine has been determined by neutron activation analysis, electrochemical analysis and by inductively coupled plasma mass spectrometry.