RADIONUCLIDE TRACER PROFILES AT THE CESAR ICE STATION AND CANADIAN-ICE-ISLAND IN THE WESTERN ARCTIC-OCEAN

Water column profiles of naturally-occurring (Pb-210, Po-210, Ra-226) and fallout (Cs-137, Pu-239,Pu-240) radionuclides measured at the Cana dian Ice Island in 1985, 1986 and 1989 over the Arctic Ocean continent al shelf were compared to profiles measured at the CESAR ice station i n the central Arctic Ocean in 1983. Cesium-137 concentrations at CESAR decreased from a mean value of 4.2 Bq/m(3) in the surface mixed layer to less than 1.0 Bq/m(3) in the Atlantic layer and deep waters. Cesiu m-137 concentrations were similar to CESAR values in the surface mixed layer at the Ice Island, but in halocline water they were lower than values measured at comparable water depths at CESAR, indicating that t he arrival of fallout Cs-137 in the Ice Island halocline had been dela yed compared to its arrival in the CESAR halocline. These data are con sistent with a combination of mixing box and lateral advection models with mixing occurring over the Russian continental shelves followed by lateral advection through the interior halocline waters of the Canada Basin. Dissolved Pb-210 and Po-210 concentrations were higher in nutr ient maximum water at the Ice Island compared to CESAR. Low values at CESAR are caused by scavenging of particle-reactive radionuclides duri ng modification of Bering Sea water in continental shelf environments. The elevated Pb-210 and Po-210 concentrations measured in nutrient ma ximum water at the Ice Island are assumed to result from ingrowth of P b-210 from Ra-226 during lateral advection of upper halocline water be tween the CESAR and Ice Island locations, a process that is estimated to take approximately 11 years. Plutonium-239,240 is also depleted, re lative to Cs-137 in the surface mixed layer and upper halocline at the Ice Island owing to its scavenging during modification of Pacific wat er in shelf environments. The Pu-239,Pu-240/Cs-137 ratio increases to values approaching fallout levels in lower halocline and Atlantic wate r owing to both reduced Pu-239,Pu-240 removal in source waters and ver tical transport of Pu-239,Pu-240 with winking particles.