The distribution of iodine in the Baltic Sea during summer

Abstract

Iodate and total inorganic iodine concentrations have been measured in near surface and intermediate waters (0–200 m) of the Baltic Sea, south of latitude 59°N, during August 1999. Additionally, organic-iodine was measured at seven selected stations in August 2000. Overall, iodine's behaviour is not conservative and is consistent with its pattern of biogeochemical cycling observed elsewhere in the oceans coupled with the particular hydrographic characteristics of this fjord. Thus, total inorganic iodine concentrations rationalised to salinity 35 were higher (∼0.60 μM) in waters on the bottom or at about 200 m, above the Deeps, presumably as a result of re-mineralisation. Meanwhile, iodate was more concentrated near the surface than on the bottom, suggesting iodate reduction in the near bottom waters. Despite the overall non-conservative pattern, in much of the water body total inorganic iodine appeared to mix conservatively between water outside the main, Darss Sill (ΣI=0.16 μM, 13 S) and that within the Sea, itself (ΣI=0.09 μM, 6 S). Meanwhile, iodate concentrations were high in the intruding water but very low behind the sills (∼0.04 μM), showing little change at salinities less than 12. Organic iodine was generally low (0.010 μM) but as high as 0.040 μM at 60 m at one station.