Enhanced particle scavenging in deep water of the Aleutian Basin revealed by 210Po-210Pb disequilibria

Abstract

The high sedimentation rate but low primary production in surface ocean raised a question whether particles from local upper water column could support high deposition in the Aleutian Basin. Here we first present large 210Po-210Pb disequilibria in deep water of the Aleutian Basin. Dissolved 210Po and 210Pb were depleted relative to 210Pb and 226Ra, respectively, in deep water below 1000 m, as well as decreased with depth, suggesting enhanced particle scavenging in the deep water. The 210Po residence times (1-2 a) in deep water were comparable to those in the upper water column, indicating that 210Po scavenging rates were high in deep water of the Aleutian Basin. The export fluxes of 210Po from the upper 100 m were estimated to be 0.2-0.8 Bq/m2/d, much lower than those in the deep water (7-8 Bq/m 2/d). Similarly, POC export fluxes in deep water (24-80 mmolC/m 2/d) were higher than those in the upper 100 m (1 mmolC/m 2/d). Such a large discrepancy between the upper and deep water suggested that particles from local upper water column could not totally meet the enhanced scavenging in the deep water. Based on mass balance calculations, the extra fluxes of 210Pb and POC imported to deep water were estimated to be 8-12 Bq/m2/d and 22-79 mmolC/m2/d, respectively. The ratio of POC to particulate 210Pb (i.e., POC/PPb) in the extra source was estimated to be 6.5 mmol/Bq, which was lower than that in the Bering Shelf with a mean POC/PPb ratio of 10.9 mmol/Bq, implying that particles in the Bering Shelf could be a potential source for the enhanced particle scavenging in deep water of the Aleutian Basin. However, quantitative and detailed role of ridges and manganese from sediments in particle scavenging in the deep water was unclear, and further studies are necessary. Key Points A large 210Po deficiency in deep Aleutian Basin High export fluxes of 210Po and POC in deep water Shelf particle was responsible for intensified scavenging in deep water © 2014. American Geophysical Union. All Rights Reserved.