Gaseous elemental mercury in the marine boundary layer and air-sea flux in the Southern Ocean in austral summer

Abstract

Gaseous elemental mercury (GEM) in the marine boundary layer (MBL), and dissolved gaseous mercury (DGM) in surface seawater of the Southern Ocean were measured in the austral summer from December 13, 2014 to February 1, 2015. GEM concentrations in the MBL ranged from 0.4 to 1.9ngm−3 (mean±standard deviation: 0.9±0.2ngm−3), whereas DGM concentrations in surface seawater ranged from 7.0 to 75.9pgL−1 (mean±standard deviation: 23.7±13.2pgL−1). The occasionally observed low GEM in the MBL suggested either the occurrence of atmospheric mercury depletion in summer, or the transport of GEM-depleted air from the Antarctic Plateau. Elevated GEM concentrations in the MBL and DGM concentrations in surface seawater were consistently observed in the ice-covered region of the Ross Sea implying the influence of the sea ice environment. Diminishing sea ice could cause more mercury evasion from the ocean to the air. Using the thin film gas exchange model, the air-sea fluxes of gaseous mercury in non-ice-covered area during the study period were estimated to range from 0.0 to 6.5ngm−2h−1 with a mean value of 1.5±1.8ngm−2h−1, revealing GEM (re-)emission from the East Southern Ocean in summer.