Seasonal and spatial evasion of mercury from the western Mediterranean Sea

Artikel i vetenskaplig tidskrift, 2017

Continuous measurements of gaseous elemental mercury (GEM) in air and dissolved gaseous mercury (DGM) in surface seawater were performed during two oceanographic campaigns (Fenice 2011 (25/10-11/11) and Fenice 2012 (11-29/8)), carried out in the Tyrrhenian Sea (Fenice 211), western Mediterranean Sea and the Atlantic Ocean (Fenice 2012) as part of the GMOS project (Global Mercury Observation System). Measured GEM and DGM were used to estimate the air-sea exchange of elemental mercury by using a two-thin film gas exchange model. Measured GEM concentrations showed significantly higher values in fall (1.7 +/- 0.4 ng m(-3)) compared to summer (1.5 +/- 03 ng m(-3), p < 0.05) and average DGM concentrations were significantly higher during the autumn campaign (29 +/- 5 pg L-1) than during the summer campaign (22 +/- 9 pg L-1, p < 0.05). Results obtained in this study and in the literature suggest seasonal, spatial and yearly variations of GEM, DGM and calculated mercury flux rates in the western Mediterranean Sea. Calculated mercury flux rates in this study ranged from -5.6 and 34 ng m(-2) h(-1), influenced by high variability in measured DGM concentrations and wind speeds. Significantly higher average evasion rates were found in summer (5.3 +/- 5.9 ng m(-2) h(-1)) compared to autumn (3.7 +/- 4.2 ng m(-2) h(-1), p < 0.05). Taking into account spatial and seasonal variations in the western Mediterranean Sea, the annual emission of elemental mercury from the 578,000 km(2) large area was estimated to be 13 tons. (C) 2017 Elsevier B.V. All rights reserved.