Sources of short-lived bromocarbons in the Iberian upwelling system

S Raimund,V Rossi,B Quack,Y Bozec,Y Morel,M Vernet,V Garçon,P Morin

doi:10.5194/bg-8-1551-2011

Abstract

Abstract. Seawater concentrations of the four brominated trace gases, dibromomethane (CH2Br2), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3) were measured at different depths of the water column in the Iberian upwelling off Portugal during summer 2007. Statistical analysis of the data set revealed three distinct clusters, caused by different sea surface temperature. Bromocarbon concentrations were elevated in recently upwelled and aged upwelled waters (mean values of 30 pmol l−1 for CHBr3), while concentrations in the open ocean were significantly lower (7.4 pmol l−1 for CHBr3). Comparison with other productive marine areas revealed that the Iberian upwelling had higher halocarbon concentrations than the Mauritanian upwelling. However, the concentrations off the Iberian Peninsula were still much lower than those of coastal macroalgal-influenced waters or those of Polar regions dominated by cold water adapted diatoms. Correlations with biological variables and marker pigments indicated that phytoplankton was a source of bromocarbon in the open ocean. By contrast, in upwelled water masses along the coast, halocarbons showed weaker correlations to marker pigments but were significantly influenced by the tidal frequency. Our results indicate a strong intertidal coastal source of bromocarbon and transport by surface currents of these enriched waters towards the upwelling region.

Highlights

Oceans are a source of short-lived bromocarbons such as dibromomethane (CH2Br2), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3) via exchange processes from the ocean surface layer to the atmosphere
In this study we present seawater concentrations of CH2Br2, CHBrCl2, CHBr2Cl and CHBr3 measured during late summer 2007 along the coast off Portugal and discuss different possible sources for these trace gases
In the Mauritanian upwelling, Carpenter et al (2009) presented sea surface concentrations for the same compounds, which were comparable with those from Quack et al (2007). Both of these studies concluded that bromocarbon concentrations were elevated in the upwelling as compared to open ocean concentrations, but lower than concentrations known from macroalgae-influenced coastal regions

Summary

Introduction

Oceans are a source of short-lived bromocarbons such as dibromomethane (CH2Br2), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3) via exchange processes from the ocean surface layer to the atmosphere. Macroalgae and phytoplankton are the main sources for oceanic bromocarbons (Manley et al, 1992; Moore et al, 1996; Carpenter and Liss, 2000; Butler et al, 2007) and algal species composition and productivity influence spatial and temporal distribution of halocarbons on a global scale (Carpenter et al, 2005). Haloperoxidase-containing phytoplankton species have been held responsible for elevated halocarbon concentrations in both laboratory experiments (Moore et al, 1996) and Published by Copernicus Publications on behalf of the European Geosciences Union

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