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Enhanced particle scavenging in deep water of the Aleutian Basin revealed by 210 Po‐ 210 Pb disequilibria
Author(s) -
Hu Wangjiang,
Chen Min,
Yang Weifeng,
Zhang Run,
Qiu Yusheng,
Zheng Minfang
Publication year - 2014
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2014jc009819
Subject(s) - water column , scavenging , deep water , particulates , geology , sedimentation , deposition (geology) , structural basin , oceanography , chemistry , geomorphology , sediment , organic chemistry , biochemistry , antioxidant
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 210 Po‐ 210 Pb disequilibria in deep water of the Aleutian Basin. Dissolved 210 Po and 210 Pb were depleted relative to 210 Pb and 226 Ra, respectively, in deep water below 1000 m, as well as decreased with depth, suggesting enhanced particle scavenging in the deep water. The 210 Po residence times (1–2 a) in deep water were comparable to those in the upper water column, indicating that 210 Po scavenging rates were high in deep water of the Aleutian Basin. The export fluxes of 210 Po from the upper 100 m were estimated to be 0.2–0.8 Bq/m 2 /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 210 Pb and POC imported to deep water were estimated to be 8–12 Bq/m 2 /d and 22–79 mmolC/m 2 /d, respectively. The ratio of POC to particulate 210 Pb (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.