How do certain atmospheric aerosols affect Cu-binding organic ligands in the oligotrophic coastal sea surface microlayer?

It is still unclear how the chemical speciation of Cu in surface seawater is impacted by aerosols from various sources deposited on the sea surface, which is surprising, considering the environmental importance of Cu. Therefore, we used voltammetry to investigate Cu complexing capacity (CuCC) in the sea surface microlayer (SML) and in the underlying water (ULW) of the oligotrophic middle Adriatic Sea during February-July 2019. The focus was on the impacts of specific atmospheric processes such as open-fire biomass burning (BB), pollination season and Saharan dust intrusion. The presence of ligand class L2 (19.9-392.0, average 63.8, median 43.1) nM; log K2 (8.3-10.2, average 9.6, median 9.6) was observed in all samples, while ligand class L1 (40.5-76.1, average 53.6, median 48.9) nM; log K1 (10.3-11.1, average 10.6, median 10.5) was found in only 25% of SML samples. Throughout the period, the SML was enriched with organic ligands by a factor of up to 9.1 compared to the ULW, mainly due to the high sensitivity of the SML to specific atmospheric depositions. In addition, measurements with corresponding specific model aerosols were conducted to analyse their impacts on CuCC. Pollen directly affected CuCC in the SML by increasing the concentration of allochthonous ligands such as proteins. The deposition of BB aerosols rich in nutrients and trace metals stimulated the biological production of organic ligands, showing an indirect effect on CuCC delayed by up to two weeks. Finally, Saharan dust had a negligible impact on CuCC. This study illustrates the susceptibility of oligotrophic coastal area to the effects of pollen and open-fire BB aerosols in altering the Cu-binding organic ligands in the SML.

Sources, Ionic Composition and Acidic Properties of Bulk and Wet Atmospheric Deposition in the Eastern Middle Adriatic Region.

Atmospheric bulk and wet deposition samples were collected simultaneously at the background coastal site in the Eastern Middle Adriatic region in order to assess the impact of major ions (Cl-, NO3-, SO42-, Na+, K+, NH4+, Mg2+, Ca2+) on deposition acidity and distinguish the main sources. Higher ion levels were observed during the cold period, especially for Cl-, Na+, Mg2+ and K+. Dust intrusion caused significant increases in levels of Ca2+, Mg2+ and K+, while open-fire events increased the levels of K+. Deposition acidity showed seasonal differences as well as the influence of dust intrusion. Low ionic balance ratios indicated acidic deposition properties and the presence of organic anions. The highest neutralization ability was found for Ca2+, Na+ and NH4+. Several natural (marine, crustal) and anthropogenic sources were determined, as well as the formation of secondary aerosols. Wet deposition was characterized by higher contribution of sea salt fraction compared to bulk deposition and lower contribution of crustal fraction.

How do open coastal fire episodes' impact sea surface microlayer neuston communities?

Human-induced climate change is expected to increase the frequency and severity of vegetation fires. The Mediterranean region is considered particularly prone to fire episodes in summer. It is well known that pyrogenic particles are an important source of external nutrients for the marine environment, especially in oligotrophic areas. In this study, the plankton components of the sea surface layers were integrated to evaluate, for the first time, their dynamics over six months and their response to fire events in a typical coastal area of the Adriatic Sea. Concentrations of nutrients and organic compounds, together with plankton communities were significantly higher in the sea surface microlayer (SML, < 1 mm thick), than in the underlying water from 1 m depth. The piconeuston community and chlorophyll a responded with extreme abundance and concentration to the most intense fire event that enriched the SML with NH4+. Phytoneuston abundance increased with a delay of 2 weeks, while diversity indices decreased slightly after the fire events. The large abundances of the studied piconeuston parameters could be explained by the high availability of organic compounds and the immediate availability of NH4+, while the phytoneuston community responded to an increased NO3- concentration, triggered by the fire events. We confirmed that fast-acting marine heterotrophs are important members of biogeochemical cycles associated with fire events and that, together with phytoplankton, they are unavoidable parameters to detect environmental changes.

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 processes 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 PO43- 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 PO43- 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/PO43- 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 heterotrophic bacteria and autotrophs in the SML along with concentrations of bulk dissolved and particulate organic carbon 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 organic 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 relevant gases, mediated by the SML.

Pollution levels and deposition processes of airborne organic pollutants over the central Adriatic area: Temporal variabilities and source identification.

First data on polycyclic aromatic hydrocarbons (PAHs) and nitro-aromatic compounds (NACs) in aerosols as well as of PAHs, polychlorinated biphenyls (PCBs) and NACs in bulk and wet atmospheric deposition samples were simultaneously obtained during 6-month-long field campaign at the costal central Adriatic area. Special attention was given to open-fire biomass burning episodes as extreme events common for the overall Mediterranean coastal area in order to gain a better understanding of the atmospheric variabilities and potential sources of trace organic pollutants in coastal environments. Diesel and gasoline combustion related to land and maritime traffic as well as occasional open-fire episodes (forest fires) were found to be the dominant pollution sources of PAHs in PM10 particles. NACs were determined almost exclusively in samples affected by biomass burning episodes. Open-fire episodes had a strong contribution to the overall NACs atmospheric deposition fluxes. Several chlorinated congeners of PCBs were predominantly contributed in deposition samples.

Atmospheric deposition of biologically relevant trace metals in the eastern Adriatic coastal area.

Aerosol (PM10), bulk deposition, sea surface microlayer (SML) and underlying water (ULW) samples were collected simultaneously during a field campaign at the middle Adriatic coastal site between February and July 2019, to assess the impact of atmospheric deposition (AD) of biologically relevant trace metals (TM) (Zn, Cu, Co, Ni, Cd and Pb) on the sea surface responses in an oligotrophic coastal region. Anthropogenic emissions from continental Europe, alongside local/regional domestic heating, likely affected the concentrations of Zn, Cd and Pb in aerosols during winter-early spring, while traffic emissions during the tourist season impacted Ni, Co and Cu aerosol concentrations. Additionally, open-fire biomass burning (BB) episodes caused considerable TM concentration increases, while Saharan dust intrusion in spring led to a 10-fold increase in Co concentrations in PM10 samples. These intensive episodes significantly affected the bulk deposition fluxes of TMs, showing that a small number of such extreme events, common to Mediterranean coastal areas, could be responsible for most of the AD. Enrichments and concentrations of total TMs in SML samples collected following BB events indicated that such events, along with high precipitation, influenced TM partitioning in surface water layers. We estimated that AD represents a significant source of TM to the shallow middle Adriatic coastal area, highlighting the need to further explore the atmosphere-sea surface links, to expand our understanding of the biogeochemistry of these important micronutrients and pollutants, including their impact on the aquatic community.