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Seasonal and daily variation of mercury evasion at coastal and off shore sites from the Mediterranean Sea

Journal article
Authors Maria Andersson
Katarina Gårdfeldt
Ingvar Wängberg
F. Sprovieri
N. Pirrone
Oliver Lindqvist
Published in Marine Chemistry
Volume 104
Issue 3-4
Pages 214-226
Publication year 2007
Published at Department of Chemistry
Centre for Environment and Sustainability
Pages 214-226
Language en
Links dx.doi.org/000246052200007
Keywords mercury, evasion, Mediterranean Sea, biogeochemistry, in situ, measurements, gas exchange, DISSOLVED GASEOUS MERCURY, ST-LAWRENCE-RIVER, ELEMENTAL MERCURY, ATMOSPHERIC MERCURY, HUMIC SUBSTANCES, NATURAL-WATERS, AIR EXCHANGE, GAS-EXCHANGE, CO2 FLUXES, WIND-SPEED
Subject categories Chemical Sciences

Abstract

Dissolved gaseous mercury (DGM) was measured continuously using two newly developed techniques and a manual technique. The continuous techniques were based on the equilibrium between the aqueous and gaseous phase (DGM = Hg-extr / H', Hg-extr is the measured mercury concentration in the gas phase, H' is the Henry's Law coefficient at the desired temperature). In order to calculate the annual mercury evasion from the Mediterranean Sea, diurnal and seasonal measurements of DGM, total gaseous mercury in air (TGM), water temperature and wind speed were performed. During August 2003, March-April 2004 and October-November 2004 measurements of these parameters were conducted on board the RV Urania. The continuous measurements of DGM showed a diurnal variation in concentration, at both coastal and off shore sites, with higher concentrations during daytime than nighttime. The concentration difference could be as large as 130 fM between day and night. The degree of saturation was calculated directly from the measurements, S = Hg-extr / TGM and was found to vary between the different seasons. The highest average degree of saturation (850%) and the largest variation in saturation (600-1150%) was observed during the summer. The spring showed the lowest variation (260-360%) and the lowest average degree of saturation (320%). The autumn also showed a large variation in saturation (500-1070%) but a lower average (740%) compared to the summer cruise. This might be explained by the temperature difference between the different seasons, since that parameter varied the most. The flux from the sea surface was calculated using the gas exchange model developed by Nightingale et al. [Nightingale, P.D., Malin, G., Law, C.S., Watson, A.J., Liss, P. S., Liddicoat, M.I., Boutin, J., Upstill-Goddard, R. C., 2000. In situ evaluation of air-sea gas exchange parameterization using novel conservative and volatile tracers. Global Biogeochemical Cycles, 14(l):373-387]. The evasion varied between the different seasons with the highest evasion during the autumn, 24.6 pmol m(-2) h(-1). The summer value was estimated to 22.3 pmol m(-2) h(-1) and the spring to 7.6 pmol m(-2) h(-1). Using this data the yearly evasion from the Mediterranean Sea surface was estimated to 77 tons. (C) 2006 Elsevier B.V. All rights reserved.

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