engleski

Variabilities of biochemical properties of the sea surface microlayer: Insights to the atmospheric deposition impacts

Atmospheric deposition (AD) of nutrients and its impact on the sea surface requires consideration of interfacial pro￾cesses within the sea surface microlayer (SML), the ocean-atmosphere boundary layer of major importance for many global biogeochemical and climate-related processes. This study comprised a comprehensive dataset, including dissolved NO3 −, NH4 + and PO4 3− in ambient aerosol particles, wet deposition and sea surface samples collected from February to July 2019 at a central Adriatic coastal site. The aerosol mean concentration of dissolved nitrogen (DIN = NO3 − + NH4 +) and PO4 3− were 48.8 ± 82.8 μmol m−3 and 0.8 ± 0.6 μmol m−3 , respectively, while their total fluxes (dry + wet) ranged from 24.2 to 212.3 μmol m−2 d−1 (mean 123.2 ± 53.2 μmol m−2 d−1 ) and from 1.2 to 2.1 μmol m−2 d−1 (mean 1.5 ± 0.3 μmol m−2 d−1 ), respectively. Intensive local episodes of open biomass burning (BB) significantly increased aerosol DIN concentrations as well as DIN deposition fluxes, particularly altering the molar DIN/PO4 3− ratio of atmospheric samples. The DIN temporal patterns showed high variability in the SML (range 0.2–24.6 μmol L−1 , mean 5.0 ± 7.1 μmol L−1 ) in contrast to the underlying water samples (range 0.5–4.2 μmol L−1 , mean 1.9 ± 1.2 μmol L−1 ), with significant increases during BB periods. Variability in abundance of het￾erotrophic bacteria and autotrophs in the SML along with concentrations of bulk dissolved and particulate organic car￾bon as well as dissolved and particulate lipids and carbohydrates, gel particles and surfactants followed DIN enhancements with a two-week delay. This study showed that AD can affect the short-term scale enrichments of or￾ganic matter in the SML, especially when accompanied by BB emissions typical of the overall Mediterranean coastal environment. This could have strong implications for global air-sea exchange processes, including those of climate rel￾evant gases, mediated by the SML.

Adriatic Sea ; Aerosol particles ; Air-sea interface ; Biomass burning ; Deposition flux ; Nutrients ; Organic matter

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