Seasonal and spatial evasion of mercury from the western Mediterranean Sea


Continuous measurements of gaseous elemental mercury (GEM) in air and dissolved gaseous mercury (DGM) in surface seawaterwere 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±0.3 ngm−3, p b 0.05) and average DGMconcentrations were significantly higher during the autumn campaign (29 ± 5 pg L−1) than during the summer campaign (22 ± 9 pg L−1, p b 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 andwind speeds. Significantly higher average evasion rateswere found in summer (5.3±5.9 ngm−2 h−1) compared to autumn (3.7 ± 4.2 ng m−2 h−1, p b 0.05). Taking into account spatial and seasonal variations in the westernMediterranean Sea, the annual emission of elemental mercury fromthe 578,000 km2 large areawas estimated to be 13 tons.

Keywords: DGM, GEM, Mercury Flux, Mediterranian Sea, Seasonal variation, Gas exchange models

Year: 2017.0

Report number: A2264

Published in: Marine Chemistry 193 (2017) 34–43