Elemental Mercury Concentrations and Fluxes in the Tropical Atmosphere and Ocean

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• 作者：Anne L. Soerensen ; Robert P. Mason ; Prentiss H. Balcom ; Daniel J. Jacob ; Yanxu Zhang ; Joachim Kuss ; Elsie M. Sunderland
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：October 7, 2014
• 年：2014
• 卷：48
• 期：19
• 页码：11312-11319
• 全文大小：385K
• ISSN：1520-5851

文摘

Air鈥搒ea exchange of elemental mercury (Hg⁰) is a critical component of the global biogeochemical Hg cycle. To better understand variability in atmospheric and oceanic Hg⁰, we collected high-resolution measurements across large gradients in seawater temperature, salinity, and productivity in the Pacific Ocean (20掳N-15掳S). We modeled surface ocean Hg inputs and losses using an ocean general circulation model (MITgcm) and an atmospheric chemical transport model (GEOS-Chem). Observed surface seawater Hg⁰ was much more variable than atmospheric concentrations. Peak seawater Hg⁰ concentrations (鈭?30 fM) observed in the Pacific intertropical convergence zone (ITCZ) were 鈭?-fold greater than surrounding areas (鈭?0 fM). This is similar to observations from the Atlantic Ocean. Peak evasion in the northern Pacific ITCZ was four times higher than surrounding regions and located at the intersection of high wind speeds and elevated seawater Hg⁰. Modeling results show that high Hg inputs from enhanced precipitation in the ITCZ combined with the shallow ocean mixed layer in this region drive elevated seawater Hg⁰ concentrations. Modeled seawater Hg⁰ concentrations reproduce observed peaks in the ITCZ of both the Atlantic and Pacific Oceans but underestimate its magnitude, likely due to insufficient deep convective scavenging of oxidized Hg from the upper troposphere. Our results demonstrate the importance of scavenging of reactive mercury in the upper atmosphere driving variability in seawater Hg⁰ and net Hg inputs to biologically productive regions of the tropical ocean.