Evidence for elevated levels of iodine-129 in the Deep Western Boundary Current in the Middle Atlantic Bight

Two 129I profiles from the Middle Atlantic Bight were measured. Near-surface values of 129I127I were as high as 100 × 10−12; subsurface values peaked at 1000–1500 m depth (reaching 55 × 10−12) and showed a steady increase below 2000 m (reaching 80 × 10−12 at 2600 m depth) coinciding with increasing F-1 l concentrations measured earlier at a similar depth (or σ-t) range at nearby stations. The subsurface 1291 increase below 2000 m water depth is attributed to the Deep Western Boundary Current (DWBC), and the minor maximum at 1000–1500 m is due to the Labrador Sea Water. However, while the F-11 maximum at the shallower depth was more pronounced than the deeper concentration increase, the opposite was true for 129I, in agreement with the expectation that the source region of the DWBC in the Greenland Sea is more directly connected to the 129I enriched North Sea water than is the Labrador Sea.