Atmospheric deposition of semivolatile aromatic hydrocarbons accounts for an important input of organic matter to the surface ocean. Nevertheless, the biogeochemical cycling and sinks of semivolatile aromatic hydrocarbons in the ocean remain largely uncharacterized. Here we present measurements of 64 polycyclic aromatic hydrocarbons in plankton and seawater from the Atlantic, Pacific, Indian and Southern Oceans, as well an assessment of their microbial degradation genes. Concentrations of the more hydrophobic compounds decreased when the plankton biomass was higher, consistent with the relevance of the biological pump. The mass balance for the global oceans showed that the settling fluxes of aromatic hydrocarbons in the water column were two orders of magnitude lower than the atmospheric deposition fluxes. This imbalance was high for low molecular weight hydrocarbons, such as phenanthrene and methylphenanthrenes, highly abundant in the dissolved phase. Parent polycyclic aromatic hydrocarbons were depleted to a higher degree than alkylated polycyclic aromatic hydrocarbons, and the degradation genes for polycyclic aromatic hydrocarbons were found to be ubiquitous in oceanic metagenomes. These observations point to a key role of biodegradation in depleting the bioavailable dissolved hydrocarbons and to the microbial degradation of atmospheric inputs of organic matter as a relevant process for the marine carbon cycle.
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The data sets generated during and/or analysed during the current study are included in this article (and Supplementary Information), or are available from the corresponding author on reasonable request.
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The authors thank the support of the RV Hespérides staff and UTM technicians during the cruise and Antarctic campaign. G. Caballero and M. J. Ojeda are acknowledged for technical support during the extraction and processing of the samples. This work was funded by the Spanish Government through the Malaspina 2010 (CSD2008-00077), REMARCA (CTM2012-34673), SENTINEL (CTM2015-70535-P) and ISOMICS (CTM2015-65691-R) projects. M.V.-C. acknowledges a Leonardo award from BBVA Foundation. Predoctoral fellowships from the Spanish government (A.M.-V. and P.C.), Catalan government (E.C.-G.), Spanish Oceanography Institute (C.M.) and BBVA Foundation (B.G.-G.) are acknowledged. B.G.-G., A.M.-V., M.V.-C., P.C., E.C.-G., N.B. and J.D. belong to the “Global Change and Genomic Biogeochemistry” research group funded by the Catalan Government (2017SGR800).
The authors declare no competing interests.
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González-Gaya, B., Martínez-Varela, A., Vila-Costa, M. et al. Biodegradation as an important sink of aromatic hydrocarbons in the oceans. Nature Geosci 12, 119–125 (2019) doi:10.1038/s41561-018-0285-3
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