Settling Removal Rates of PCBs into the Northwestern Atlantic Derived from 238U-234Th Disequilibria

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• 作者：Ö ; rjan Gustafsson ; Philip M. Gschwend ; and Ken O. Buesseler
• 刊名：Environmental Science & Technology
• 出版年：1997
• 出版时间：December 1997
• 年：1997
• 卷：31
• 期：12
• 页码：3544 - 3550
• 全文大小：151K
• 年卷期：v.31,no.12(December 1997)
• ISSN：1520-5851

文摘

Surface ocean export fluxes of polychlorinated biphenyls(PCBs) were deduced utilizing ²³⁴Th as an indicator oftheremoval rates of particle-bound species from coastal,continental shelf, and pelagic surface waters. Thefractionof the PCB settling flux that reaches the sediments (theratioof bottom sediment import flux to ²³⁴Th-derivedsurfaceocean export flux) decreased with both water column depthand with aqueous solubility of the congeners, presumablyas a result of particle decomposition and/or compounddesorption. A sharper decrease in ²³⁴Th-derivedsurfaceocean fluxes away from the continental source was seenfor congeners with increasing chlorination. Thissuggeststhat atmospheric washout followed by particle-mediatedsettling out of the surface ocean are the predominantprocesses affecting the PCBs, as opposed to atmospherichydroxyl radical-mediated decomposition. Based onthislimited data set, the largest fraction of each PCB isremovedinto the open ocean, although higher areal fluxes are seencloser to the coast. For example, we estimate that14 000mol yr^-1 of a tetrachlorobiphenyl (congener52) weresequestered in the northwestern Atlantic Ocean in 1993-1994, with 75% of the flux being in the pelagic sector,20%on the continental shelf, and only 5% in the 20-km-widecoastal region closest to the continentalsource.