Deciphering the Role of Water Column Redoxclines on Methylmercury Cycling Using Speciation Modeling and Observations From the Baltic Sea - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Global Biogeochemical Cycles Année : 2018

Deciphering the Role of Water Column Redoxclines on Methylmercury Cycling Using Speciation Modeling and Observations From the Baltic Sea

Résumé

Oxygen-​depleted areas are spreading in coastal and offshore waters worldwide, but the implication for prodn. and bioaccumulation of neurotoxic methylmercury (MeHg) is uncertain. We combined observations from six cruises in the Baltic Sea with speciation modeling and incubation expts. to gain insights into mercury (Hg) dynamics in oxygen depleted systems. We then developed a conceptual model describing the main drivers of Hg speciation, fluxes, and transformations in water columns with steep redox gradients. MeHg concns. were 2-​6 and 30-​55 times higher in hypoxic and anoxic than in normoxic water, resp., while only 1-​3 and 1-​2 times higher for total Hg (THg)​. We systematically detected divalent inorg. Hg (HgII) methylation in anoxic water but rarely in other waters. In anoxic water, high concns. of dissolved sulfide cause formation of dissolved species of HgII: HgS2H-​(aq)​ and Hg (SH)​20(aq)​. This prolongs the lifetime and increases the reservoir of HgII readily available for methylation, driving the high MeHg concns. in anoxic zones. In the hypoxic zone and at the hypoxic-​anoxic interface, Hg concns., partitioning, and speciation are all highly dynamic due to processes linked to the iron and sulfur cycles. This causes a large variability in bioavailability of Hg, and thereby MeHg concns., in these zones. We find that zooplankton in the summertime are exposed to 2-​6 times higher MeHg concns. in hypoxic than in normoxic water. The current spread of hypoxic zones in coastal systems worldwide could thus cause an increase in the MeHg exposure of food webs.
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Dates et versions

hal-01982384 , version 1 (15-01-2019)

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A. Soerensen, A. Schartup, A. Skrobonja, Sylvain Bouchet, David Amouroux, et al.. Deciphering the Role of Water Column Redoxclines on Methylmercury Cycling Using Speciation Modeling and Observations From the Baltic Sea. Global Biogeochemical Cycles, 2018, 32 (10), pp.1498-1513. ⟨10.1029/2018gb005942⟩. ⟨hal-01982384⟩
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