| Summary: | Using a method which simultaneously concentrates and isolates Pb from seawater, a total of 208 samples collected using trace-metal clean techniques were determined for dissolved Pb concentration in the subarctic Northeast Pacific and the Canada Basin of the southwestern Arctic Ocean. The analytical method found good agreement between determined values and consensus values of several seawater standards. Concentration in seawater was generally dictated by proximity to pollution sources which appeared to provide Pb via aeolian deposition and by proximity to primary productivity or freshly precipitated mineral phases which scavenged Pb to lower levels than expected based on previous research. Over the entire dataset, concentration ranged from 1.8 pmol/kg to 81.3 pmol/kg, with the highest values occurring just below the permanent mixed layer in the northeast Pacific and was of unknown origin. The lowest level was found in the Pacific water mass of the southern Beaufort Sea, which may be the result of interactions with sediment during transit through the Bering and Chukchi Seas. When samples that were expected to be contaminated are discounted, Pb levels were generally lowest in the Arctic, below 30 pmol/kg. Samples taken from three eddies along the British Columbian and southern Alaskan coasts found low [Pb] within the eddy relative to reference stations, though in two of the eddies a phytoplankton bloom had not occurred, suggesting that either the source water was low in Pb or scavenging had occurred by sorption onto precipitated mineral phases during estuarine processes. A low- resolution time series between 1992 and 2010 at Ocean Station Papa (OSP; 50°N, 145°W) found that Pb concentration at this location has remained quite steady over time, in contrast with the North Atlantic Ocean which showed a drastic decrease in concentration over the same time period. The difference may be attributed to formation of the water mass in the Sea of Okhotsk during the winter when atmospheric conditions would transport most Asian pollution away from the region where the water mass subducts and advects towards OSP, along with a different history of Pb pollution upwind of the Atlantic and Pacific Oceans.
|
|---|