Articles | Volume 16, issue 18
Atmos. Chem. Phys., 16, 12219–12237, 2016

Special issue: Biogeochemical processes, tropospheric chemistry and interactions...

Atmos. Chem. Phys., 16, 12219–12237, 2016

Research article 29 Sep 2016

Research article | 29 Sep 2016

Biogenic halocarbons from the Peruvian upwelling region as tropospheric halogen source

Helmke Hepach1,a, Birgit Quack1, Susann Tegtmeier1, Anja Engel1, Astrid Bracher2,3, Steffen Fuhlbrügge1, Luisa Galgani1,b, Elliot L. Atlas4, Johannes Lampel5, Udo Frieß5, and Kirstin Krüger6 Helmke Hepach et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
  • 2Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • 3Institute of Environmental Physics, University of Bremen, Bremen, Germany
  • 4Rosenstiel School of Marine and Atmospheric Science (RSMAS), University of Miami, Miami, USA
  • 5Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany
  • 6Department of Geosciences, University of Oslo, Oslo, Norway
  • anow at: Environment Department, University of York, York, UK
  • bnow at: Department of Biotechnology, Chemistry and Pharmacy, University of Siena, Siena, Italy

Abstract. Halocarbons are produced naturally in the oceans by biological and chemical processes. They are emitted from surface seawater into the atmosphere, where they take part in numerous chemical processes such as ozone destruction and the oxidation of mercury and dimethyl sulfide. Here we present oceanic and atmospheric halocarbon data for the Peruvian upwelling zone obtained during the M91 cruise onboard the research vessel METEOR in December 2012. Surface waters during the cruise were characterized by moderate concentrations of bromoform (CHBr3) and dibromomethane (CH2Br2) correlating with diatom biomass derived from marker pigment concentrations, which suggests this phytoplankton group is a likely source. Concentrations measured for the iodinated compounds methyl iodide (CH3I) of up to 35.4 pmol L−1, chloroiodomethane (CH2ClI) of up to 58.1 pmol L−1 and diiodomethane (CH2I2) of up to 32.4 pmol L−1 in water samples were much higher than previously reported for the tropical Atlantic upwelling systems. Iodocarbons also correlated with the diatom biomass and even more significantly with dissolved organic matter (DOM) components measured in the surface water. Our results suggest a biological source of these compounds as a significant driving factor for the observed large iodocarbon concentrations. Elevated atmospheric mixing ratios of CH3I (up to 3.2 ppt), CH2ClI (up to 2.5 ppt) and CH2I2 (3.3 ppt) above the upwelling were correlated with seawater concentrations and high sea-to-air fluxes. During the first part of the cruise, the enhanced iodocarbon production in the Peruvian upwelling contributed significantly to tropospheric iodine levels, while this contribution was considerably smaller during the second part.

Short summary
We present surface seawater measurements of bromo- and iodocarbons, which are involved in numerous atmospheric processes such as tropospheric and stratospheric ozone chemistry, from the highly productive Peruvian upwelling. By combining trace gas measurements, characterization of organic matter and phytoplankton species, and tropospheric modelling, we show that large amounts of iodocarbons produced from the pool of organic matter may contribute strongly to local tropospheric iodine loading.
Final-revised paper