Features and influencing mechanisms of gaseous elemental mercury over the equatorial Pacific and their differences with the Southern Ocean

Due to the harmful impacts on the ecosystem and even human health, mercury (Hg) compounds in the environment deserve serious concern. Atmospheric mobilization and exchange at the air-sea interface are important processes in biogeochemical cycling of Hg. Relying on the 30th (2013/2014), 31st (2014/2015), and 33rd (2016/2017) Chinese National Antarctic Research Expedition aboard R/V Xuelong, we found significant rising gaseous elemental mercury (GEM) concentrations over the equatorial Central Indo-Pacific region. Excluding the contribution of anthropogenic, volcanic and biomass burning emissions, the enhanced GEM in marine boundary layer was likely due to the combined actions of two driving factors drove by the Inter-Tropical Conversion Zone (ITCZ): (1) intense wet deposition of Hg, followed by subsequent rapid photoreduction and vast evasion from the surface sea; and (2) the regional low-level convergence of airflow that caused the mass accumulation of GEM in air. In addition, apparently higher GEM concentration level in the equatorial Central Indo-Pacific than in the Southern Ocean was observed in one cruise. Further investigation suggests that apart from the ITCZ corresponded mechanisms, the effects of spatial differences in anthropogenic emissions and more significant GEM oxidation in Antarctic sea should play roles in this phenomenon