Preprints
https://doi.org/10.5194/acp-2022-832
https://doi.org/10.5194/acp-2022-832
 
19 Dec 2022
19 Dec 2022
Status: this preprint is currently under review for the journal ACP.

Amino acids, carbohydrates and lipids in the tropical oligotrophic Atlantic Ocean: Sea-to-air transfer and atmospheric in situ formation

Manuela van Pinxteren1, Sebastian Zeppenfeld1, Khanneh Wadinga Fomba1, Nadja Triesch1,a, Sanja Frka2, and Hartmut Herrmann1 Manuela van Pinxteren et al.
  • 1Atmospheric Chemistry Department (ACD), Leibniz-Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany
  • 2Division for Marine and Environmental Research, Ruđer Bošković Institute, 10000 Zagreb, Croatia
  • anow at: Department Safety in the Food Chain, German Federal Institute for Risk Assessment, 10589 Berlin, Germany

Abstract. This study examines carbohydrates, amino acids, and lipids as important contributors to organic carbon (OC) in the tropical Atlantic Ocean at the Cape Verde Atmospheric Observatory (CVAO). The above compounds were measured in both surface seawater and in ambient submicron aerosol particles to investigate their sea-to-air transfer, including their enrichment in the sea surface microlayer (SML), potential atmospheric in situ formation or degradation, and their oceanic contribution to the ambient marine aerosol particles.

In bulk seawater and the SML, similar distributions among species were found for the lipids and carbohydrates with moderate SML enrichments (enrichment factor EFSML = 1.3±0.2 and 1.1±0.5 respectively). In contrast, the amino acids exhibited a higher enrichment in the SML with an averaging EFSML of 2.4±0.3 although being less surface-active than lipids. The same compounds studied in the seawater were found on the ambient submicron aerosol particles whereas the lipids were more pronounced enriched (EFaer. = 1.6x105) compared to the amino acids and carbohydrates (EFaer. = 1.5x103 and 1.3x103 respectively), likely due to their high surface activity and/or the lipophilic character. Detailed molecular analysis of the seawater and aerosol particles revealed changes in the relative composition of the single organic compounds. They were most pronounced for the amino acids and are likely related to an in situ atmospheric processing by biotic and/or abiotic reactions.

On average 49 % of the OC on the aerosol particles (≙ 97 ng m-3) could be attributed to the specific components or component groups investigated in this study. The majority (43 %) was composed of lipids. Carbohydrates and amino acids made up less than 1 % of the OC. This shows that carbohydrates, at least resolved via molecular measurements of single sugars, do not comprise a very large fraction of OC on marine aerosol particles, in contrast to other studies. However, carbohydrate-like compounds are also present in the high lipid fraction (e.g., as glycolipids), but their chemical composition could not be revealed by the measurements performed here.

Previously determined OC components at the CVAO, in detail amines, oxalic acid, and carbonyls, comprised an OC fraction of around 6 %.

Since the identified compounds constituted about 50 % of the OC and belong to the rather short-lived biogenic material probably originating from the surface ocean, a pronounced coupling between ocean and atmosphere was indicated for this oligotrophic region. The remaining, non-identified OC fraction might in part contain recalcitrant OC, however, this fraction does not constitute the vast majority of OC in the here investigated aerosol particles.

Manuela van Pinxteren et al.

Status: open (until 12 Feb 2023)

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Manuela van Pinxteren et al.

Manuela van Pinxteren et al.

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Short summary
Important marine organic carbon compounds were identified in the Atlantic Ocean and marine aerosol particles. These compounds were strongly enriched in the atmosphere. Their enrichment was, however, not solely explained with sea-to-air transfer but also via atmospheric in situ formation. The identified compounds constituted about 50 % of the organic carbon on the aerosol particles and a pronounced coupling between ocean and atmosphere for this oligotrophic region could be concluded.
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