129I in the Baltic Proper and Bothnian Sea: application for estimation of water exchange and environmental impact.

We report here new data and a mass balance model for (129)I in the Baltic Proper and the Bothnian Sea covering the period from November-December 2009. The results showed that the general (129)I concentrations in the Bothnian Sea were two-four folds lower than in the Baltic Proper for both surface and deep water. Water exchange between the two basins based on the (129)I mass balance model suggests fluxes from the Baltic Proper to the Bothnian Sea and vice versa at 980 km(3)/y (600-1400 km(3)/y) and 1180 km(3)/y (780-1600 km(3)/y) respectively. Water retention time (residence time) in the Bothnian Sea was estimated at up to 4 years. Applying the (129)I exchange model, an estimate of total phosphorus and nitrogen inflow from the Baltic Proper to the Bothnian Sea indicates values of 20 ± 7 × 10(3) tons/y and 300 ± 50 × 10(3) tons/y respectively. The values for the outflow from the Bothnian Sea to the Baltic Proper hold 12 ± 3 × 10(3) tons/y for total phosphorus and 283 ± 55 × 10(3) tons/y for total nitrogen. These data and application of (129)I as a tracer of water masses provide information on small scale salinity changes which are vital for accurate understanding of the Baltic Sea ecosystems evolution through time.