Halocarbons are produced naturally in the oceans by biological andchemical processes. They are emitted from surface seawater into theatmosphere, where they take part in numerous chemical processes such as ozonedestruction and the oxidation of mercury and dimethyl sulfide. Here wepresent oceanic and atmospheric halocarbon data for the Peruvian upwellingzone obtained during the M91 cruise onboard the research vessel in December 2012. Surface waters during the cruise werecharacterized by moderate concentrations of bromoform (CHBr) anddibromomethane (CHBr) correlating with diatom biomass derivedfrom marker pigment concentrations, which suggests this phytoplankton groupis a likely source. Concentrations measured for the iodinated compounds methyliodide (CHI) of up to 35.4 pmol L, chloroiodomethane(CHClI) of up to 58.1 pmol L and diiodomethane (CHI)of up to 32.4 pmol L in water samples were much higher than previouslyreported for the tropical Atlantic upwelling systems. Iodocarbons alsocorrelated with the diatom biomass and even more significantly with dissolvedorganic matter (DOM) components measured in the surface water. Our resultssuggest a biological source of these compounds as a significant driving factorfor the observed large iodocarbon concentrations. Elevated atmospheric mixingratios of CHI (up to 3.2 ppt), CHClI (up to 2.5 ppt) andCHI (3.3 ppt) above the upwelling were correlated with seawaterconcentrations and high sea-to-air fluxes. During the first part of thecruise, the enhanced iodocarbon production in the Peruvian upwellingcontributed significantly to tropospheric iodine levels, while thiscontribution was considerably smaller during the second part.
展开▼
