Steady-state mixing of iodine in shelf seas off the British Isles

A study of dissolved iodate and total iodine on the Hebridean shelf in several months of 1995/6 confirms an earlier hypothesis that the distribution of iodine in these waters is almost in steady state throughout the year. No evidence was found for changes in iodine chemistry that might correlate with seasonal changes in primary productivity, and the inappropriateness of adopting a Redfield-type model to explain the main trend of the iodine distribution is discussed. The system is determined by the mixing of three water types. To the west, the iodine distribution is governed by water of the North Atlantic Current (typically with salinity of 35.3 and iodate and total iodine concentrations close to 0.40 and 0.45 μM, respectively, and its mixing with deeper water containing a slightly higher concentration of iodate, but similar salinity. To the east, the distribution is governed by coastal waters with low salinity (∼33) and low iodate concentration (0.25 μM) but only a marginally lower total iodine concentration. The approximate iodate concentration, rationalised to 35 salinity, is given by RIO3=0.060e−22 (35.42−S)+0.37e−0.20 (35.42−S)+0.010e−0.010 (35.42−S). Rationalised total iodine varied by only about 5%. Reasons are given for believing that the conditions found in the Hebridean waters probably applies to the whole of the shelf-seas of Britain, including the North Sea.