²¹⁰Po-²¹⁰Pb Disequilibria In Polar Seas In Summer

Water samples were collected during the28th Chinese Antarctic Research Expedition and the5th Arctic Research Expedition in2012summer. Biogeochemical cycle of210Po and210Pb were studied in the polar seas. The particle dynamics were revealed and particulate organic carbon (POC) export fluxes were evaluated in the Antarctic Peninsula sea areas and Bering Sea.The total210Po activity concentrations ranged from0.74to3.17Bq/m3with an average of1.79Bq/m3in the Antarctic Peninsula sea areas. Dissolved210Po accounted for50%～91%of the total210Po with an average of93%. Dissolved210Po is the main form of210Po in study areas. Total210Pb activity concentrations ranged from1.40to5.08Bq/m3with an average of2.93Bq/m3. On average, dissolved2I0Pb accounted for88%of the total210Pb. Dissolved210Pb is the main form of210Pb in study areas.Higher210Po activity concentrations and210Po/210Pb activity ratios were found in abyssal areas compared to the slope regions in the Antarctic Peninsula seas. The scavenging and removal fluxes, and residence times of210Po and210Pb were calculated via210Po-210Pb disequilibria. The long residence times of210Po were found in the abyssal areas with an average of2.07a, compared to the slope regions with an average of0.63a. Our results suggested that the scavenging and removal of210Po on the slope regions was more efficient than that in the abyssal areas.The maximum of total210Pb was observed in the middle waters (100-500m) with an equilibria or excess relative to226Ra. The unique phenomenon showed an additional input of Pb. The atmospheric deposition may be the most possible source.2Pb were deposited to seawater or sea ice surfaces through atmosphere in the south hemisphere in winter. The deep water was influenced by intense water mixing, and thus the characteristics with high2I0Pb and210Pb/226Ra>1were observed in winter water masses in summer.The POC export fluxes at100m and411m were estimated to be0.73and11.01mmolC/m2/d at station D4-3in the Antarctic Peninsula slope via210Po-210Pb disequilibria. The POC export fluxes at500m and3393m were estimated to be39.29and65.64mmolC/m2/d at station D4-9in the Antarctic Peninsula abyssal. The POC export fluxes increased with the depth, indicating POC export was influenced by other processes besides settling from the upper ocean.The total’Po activity concentrations ranged from below detection to2.58Bq/m3with an average of0.56Bq/m3in the Bering Sea and Chukchi Sea. Total210Pb activity concentrations ranged from0.37to3.68Bq/m3with an average of1.15Bq/m3. Po activity concentrations showed a spatial variation with a characteristic as follow: the Bering Sea slope> the Bering Sea shelf> the Chukchi shelf. Similarly,210Pb activity concentrations showed a spatial variation with a characteristic as follow:the Bering Sea slope> the Bering Sea shelf-the Chukchi shelf. The ratios of dissolved210Po to total210Po showed a spatial variation with a characteristic as follow:the Bering Sea slope (75%)> the Bering Sea shelf (47%)-the Chukchi shelf (50%). Similarly, the ratios of dissolved210Pb to total210Pb showed a spatial variation with a characteristic as follow:the Bering Sea slope (67%)> the Bering Sea shelf (56%)-the Chukchi shelf (56%).The scavenging and removal fluxes, and residence times of210Po and210Pb in the Bering Sea and Chukchi Sea were calculated via210Po-210Pb disequilibria. The long residence times of210Po were found in the Bering slope with an average of1.42a compared to the Bering shelf with an average of0.24a. Similarly, the residence times of210Pb in the Bering slope (with an average of41.05a) were longer than those in the shelf (with an average of6.64a). The results suggested the scavenging and removal of210Po and210Pb in the shelf were more efficient than those in the slope. Hence, the intense scavenging and removal processes occurred during the Pacific inflow transporting to the Chukchi shelf from the Bering slope via Bering shelf. However, the scavenging and removal of210Po was more efficient than those of210Pb.210Pb export fluxes were estimated via210Pb mass balance in the northern Bering shelf considering both the lateral transport of upper water and sediment resuspension in bottom water. The lateral input fluxes of2l0Pb in the upper water and their ratios to total input fluxes of210Pb decreased from both the east and the west to the centeral regions, indicating that210Pb lateral export fluxes through the Anadyr Water and Alaska Coastal Water were higher than those through the Bering Shelf Water. The Alaska Coastal Water had the highest210Pb lateral flux among these three pathways. Generally, our results suggested that the Pacific inflow is an important source of210Pb in the Chukchi Sea. Besides, the scavenging and removal of Pb in the deep water was more efficient than those in the upper water, indicating the removal of Pb was enhanced by sediment resuspension.The POC export fluxes were estimated to be from0.04to2.89mmolC/m2/d with an average of1.38mmolC/m2/d via210Po-210Pb disequilibria in the northern Bering Shelf. POC export fluxes in the upper water were lower than those in deep water at some stations, indicating POC export was influenced by sediment resuspension besides settling from the upper ocean.