.sup.210Po-.sup.210Pb distribution and carbon export in the northern Gulf of Mexico continental slope.

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Authors: Wokil Bam and Kanchan Maiti
Date: June 2021
Publisher: Elsevier B.V.
Document Type: Report
Length: 415 words

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Keywords 210Po; 210Pb; Carbon export; northern Gulf of Mexico; Particle export efficiency Highlights * .sup.210Po has an average residence time of 2.18 [plus or minus] 0.47 year in the continental shelf. * .sup.210Po based POC fluxes varied between 8.59 and 37.65 mg C m.sup.-2 d.sup.-1 across the shelf. * The e-ratio varied between 0.027 and 0.11 (mean = 0.05 [plus or minus] 0.01) for this region is found to be low. * Highest reported activities of .sup.210Po and .sup.210Pb for open ocean observed in the hypersaline Orca basin. Abstract An important pathway for CO.sub.2 sinking in the ocean is via the "biological pump", driven by the production of particulate organic carbon (POC) in the surface ocean and its subsequent export to the deeper ocean via vertical settling. Here we examine the vertical fluxes of POC in the continental slope of the northern Gulf of Mexico by utilizing the short-lived radionuclide pair .sup.210Po - .sup.210Pb. The total activities of .sup.210Po and .sup.210Pb ranged from 2.5 [plus or minus] 0.35 to 16.52 [plus or minus] 1.98 dpm 100 L.sup.-1 and from 3.47 [plus or minus] 0.45 to 24.49 [plus or minus] 3.42 dpm 100 L.sup.-1 respectively with the exception of higher activities of .sup.210Po (87.36 [plus or minus] 11.38 dpm 100 L.sup.-1) and .sup.210Pb (32.25 [plus or minus] 4.35 dpm 100 L.sup.-1) from the near bottom water in the hypersaline anoxic Orca basin. In the upper 150 m of the water column, the inventories of .sup.210Pb were consistently greater than those of .sup.210Po while the total overall water column inventories of .sup.210Po and .sup.210Pb were found to be near equilibrium. The .sup.210Po fluxes varied between 9.8 [plus or minus] 6.34 dpm m.sup.-2 d.sup.-1 and 30.7 [plus or minus] 12.06 dpm m.sup.-2 d.sup.-1 with corresponding POC fluxes between 8.6 mg C m.sup.-2 d.sup.-1 and 37.65 mg C m.sup.-2 d.sup.-1. The fluxes showed a general decreasing trend further offshore, closely following a similar trend in net primary productivity across the slope. The export efficiency ratios "e-ratios" of the biological pump over this slope region was found to vary between 0.027 and 0.11 averaging at 0.05 [plus or minus] 0.01, which is low. The .sup.210Po based and the model-based e-ratio estimates were different but within the range of previous estimates. Author Affiliation: Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LA, 70803, USA * Corresponding author. Article History: Received 8 November 2020; Revised 29 March 2021; Accepted 30 March 2021 Byline: Wokil Bam [wbam1@lsu.edu] (*), Kanchan Maiti

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Gale Document Number: GALE|A663043948