Iodine-129 concentrations in marginal seas of the North Pacific and Pacific-influenced waters of the Arctic Ocean

Water sampling during the 1993 IV Russian-US Joint Expedition to the Bering and Chukchi Seas (BERPAC) indicates that Pacific Ocean burdens of the long-lived radionuclide I-129 are relatively low in the Pacific-influenced Arctic, particularly compared to high latitude waters influenced by the North Atlantic. These low concentrations occur despite the presence of potential submerged anthropogenic sources in the East Sea (Sea of Japan), and in the northwest Pacific Ocean, east of the Kamchatka Peninsula. The concentration of I-129 entering the Arctic Ocean through Bering Strait, similar to0.7 x 10(8) atoms kg(-1), is only slightly higher than observed in deep Pacific waters. Similar concentrations (0.44-0.76 x 10(8) atoms kg(-1)) measured in Long Strait indicate no significant transfer of I-129 eastward into the Chukchi Sea in the Siberian Coastal Current from the Siberian marginal seas to the west. However, the concentrations reported here are more than an order of magnitude higher than the Bering Strait input concentration estimated (1.0 X 10(6) atoms kg(-1)) from bomb fallout mass balances, which supports other existing evidence for a significant atmospheric deposition term for this radionuclide in surface ocean waters. Near-bottom water samples collected in productive waters of the Bering and Chukchi Seas also suggest that sediment regeneration may locally elevate I-129 concentrations, and impact its utility as a water mass tracer. As part of this study, two deep I-129 profiles were also measured in the East Sea in 1993-1994. The near-surface concentration of I-129 ranged from 0.12 to 0.31 x 10(8) atoms kg(-1). The I-129 concentration showed a steady decrease with depth, although because of active deep water ventilation, the entire 3000 m water column exceeded natural concentrations of the radionuclide. Atom ratios Of I-129/Cs-137 in the East Sea also suggest an excess of I-129 above bomb fallout estimates, also possibly resulting from atmospheric deposition ultimately originating from nuclear facilities. (C) 2001 Elsevier Science Ltd. All rights reserved.