Seven-year monitoring of mercury in wet precipitation and atmosphere at the Amsterdam Island GMOS station

Mercury (Hg) fate and transport research requires more effort to obtain a deep knowledge of its biogeochemical cycle, particularly in the Southern Hemisphere and Tropics that are still missing of distributed monitoring sites.Continuous monitoring of atmospheric Hg concentrations and trend worldwide is relevant for the effectiveness evaluation of the Minamata Convention on Mercury (MCM) actions. In this context, Gaseous Elemental Mercury (GEM) and total mercury (THg) in precipitations were monitored from 2013 to 2019 at the Amsterdam Island Observatory (AMS -37 degrees 48 ' S, 77 degrees 34 ' E) to provide insights into the Hg pathway in the remote southern Indian Ocean, also considering ancillary dataset of Rn-222, CO2, CO, and CH4. GEM average concentration was 1.06 +/- 0.07 ng m- 3, with a slight increase during the austral winter due to both higher wind speed over the surface ocean and contributions from southern Africa. In wet depositions, THg average concen-tration was 2.39 +/- 1.17 ng L-1, whereas the annual flux averaged 2.04 +/- 0.80 mu gm- 2 year -1. In general, both GEM and Volume-Weighted Mean Concentration (VWMC) of THg did not show an increasing/decreasing trend over the seven-year period, suggesting a substantial lack of evolution about emission of Hg reaching AMS.Air masses Cluster Analysis and Potential Source Contribution Function showed that oceanic evasion was the main Hg contributor at AMS, while further contributions were attributable to long-range transport events from southern Africa, particularly when the occurrence of El Nin similar to o increased the frequency of wildfires.

Automated summary

More research effort is needed to understand the biogeochemical cycle of mercury (Hg), especially in the Southern Hemisphere and Tropics where monitoring sites are lacking. Continuous monitoring of Hg concentrations worldwide is important for evaluating the effectiveness of the Minamata Convention on Mercury (MCM) actions. A study conducted at the Amsterdam Island Observatory investigated the pathways of Hg in the remote southern Indian Ocean from 2013 to 2019, revealing the contribution of oceanic evasion and long-range transport events from southern Africa.