Dissolved gaseous mercury production and sea-air gaseous exchange in impacted coastal environments of the northern Adriatic Sea

Mercury (Hg) in the “Skin” of the Ocean: Dissolved Gaseous Hg, Total Hg, and Hg Redox Chemistry in Sea Surface Microlayer and Implication for Air–Sea Hg Exchange

“…The air–sea Hg(0) fluxes fundamentally control the mass balance of the oceanic Hg cycle. , The quantification of air–sea Hg(0) fluxes is therefore one of the most critical topics of oceanic Hg science. Since the 1980s, dozens of field studies have been conducted to determine the air–sea Hg(0) fluxes cross a range of marine environments, from estuaries and bays − and coastal seas ,,,,− to the Arctic ocean , and open ocean. ,,,− At present, two methods, the DFC ,,,, and the two-layer model, ,,,,, have been applied to quantify the air–water Hg(0) fluxes. In most studies, particularly the investigations of offshore and open ocean, the two-layer model is widely applied due to its accessibility and the comparability of results among different studies. ,,,,− The two-layer model is also widely used in global Hg models to estimate Hg(0) fluxes between air and the ocean. , The principle of the two-layer model to estimate air–sea Hg(0) fluxes is based on the air–sea Hg(0) concentration difference multiplied by the gas transfer velocity. ,, Therefore, the selection of surface seawater samples for measuring DGM concentrations directly determines the Hg(0) concentration gradient between air and the ocean and subsequently influences the air–sea Hg(0) fluxes.…”

“…Recently, Floreani et al found that although the DGM concentrations in the surface waters were different in two different aquatic systems, the air−water Hg(0) fluxes determined by the dynamic flux chamber (DFC) method were comparable. 49 The results indicate the possible effect of the SML on air−water Hg(0) exchange. Due to the aforementioned unique properties of Hg, such as air−water exchange of Hg(0) and photochemical reactions of Hg, the SML Hg sampling, particularly for DGM sampling, is very challenging.…”

“…Particularly, investigators generally used DGM data of SSWs (the water depth: ∼0.2 to 10 m) to estimate air–sea Hg(0) fluxes with a two-layer model. ,,− The potential difference of Hg(0) concentrations and patterns in the SML and SSWs will lead to a possible bias in the estimate of global air–sea Hg(0) fluxes. Recently, Floreani et al found that although the DGM concentrations in the surface waters were different in two different aquatic systems, the air–water Hg(0) fluxes determined by the dynamic flux chamber (DFC) method were comparable . The results indicate the possible effect of the SML on air–water Hg(0) exchange.…”