The Mediterranean basin continuously receives anthropogenic aerosols from industrial and domestic activities from the European region, as well as high rates of aeolian material in the form of mineral dust from northern Africa. Moreover, combustion dominates over natural dust, whereas vegetation fires frequently burn throughout the Mediterranean coastal zone, especially during hot and dry summers. Once in the atmosphere, aerosols become an important external source of nutrients but also of toxins to the marine ecosystem through atmospheric deposition (AD), affecting the quality and quantity of organic matter (OM) produced by phytoplankton in the photic zone, and altering the CO2 uptake. AD onto sea surface cannot be completely understood without considering the interfacial processes within the sea surface microlayer (SML). As the uppermost millimeter of the sea surface, the SML represents the natural interface of the major environmental importance. It could serve as the first indicator of increasing human impact and climate change due to fast response of its biological and physico-chemical properties. However, surprisingly little research assessed the impact of AD on surface plankton communities, distinguishing between the SML and the water column bellow.This work is designed to assess the magnitude and temporal variability of atmospheric concentrations and deposition fluxes of nutrients and trace metals, and to gain insight into the AD impacts on the nature of enrichments of organic compounds within surface layers in a typical Mediterranean coastal environment. The field campaign was conducted during the period of retrieval of sea surface oligotrophic conditions (February-July 2019) at the Adriatic coastal area. On-line black carbon (BC) concentrations were measured while the aerosol particles (PM10), wet and total deposition samples as well as the SML and underlying water (ULW; 0.5 m depth) samples were collected simultaneously. The first comprehensive insight into concentration levels of macro nutrients (N, P) and trace metals (e.g. Cu, Pb, Cd, Ni, Zn, Co) in atmospheric samples, their transport history, source apportionment and deposition fluxes to the coastal Adriatic area will be presented. The temporal dynamics of SML biology as well as concentrations of inorganic and organic constituents enabled the assessment of their sources and the nature of the enrichments taking place within the SML. Due to their significance throughout the Mediterranean coastal area, open-fire episodes and Saharan dust inputs were especially considered. In order to better understand the impacts of ambient AD from diverse sources on the physiology and biomass of the natural plankton population and consequently on the chemistry of the surface layers (SML and ULW), we further conducted the first in situ bioassay incubation experiment of its kind at the Adriatic Sea. We experimentally examined the impact of locally collected anthropogenic aerosols, that had different levels of biologically important nutrients, trace metals and organic pollutants, in contrast to the material mimicking biomass burning events.Acknowledgment: This work has been supported by the Croatian Science Foundation under the IP-2018-01-3105 project: Biochemical responses of oligotrophic Adriatic surface ecosystems to atmospheric deposition inputs.
Surface tension is a key parameter in the Kohler equation describing cloud droplet formation, but which has been ignored for many years, mostly because of the lack of information on the surfactants present in aerosols and their effects on the surface tension. For this reason we have recently developed methods to extract the total surfactant fraction from aerosols (= sum of all the components affecting their surface tension), measure their concentrations, and determine the overall surface tension isotherm of the aerosols. This work presents the application of these methods to PM1 aerosols from different regions; Lyon, France (urban site, 55 samples), Rozgonica, Croatia (coastal site, 17 samples), and Pallas, Finland (remote site, 237 samples), and the first results on their surfactants and how much they might contribute to cloud formation.
The results show that, in spite of large differences in the concentration and size distribution of aerosols in these different regions, the average molar concentrations of anionic, cationic and non-ionic surfactants inside the PM1 particles displayed similar trends: non-ionic surfactants represented 60 to 70 % of the total surfactant concentration, anionic ones 20 to 35 %, while cationic surfactants were negligible. However, large differences were observed in the Critical Micelle Concentration (CMC), the key point of the surface tension isotherm: the CMC of surfactants in remote aerosols was nearly 10 times lower than that in urban aerosols (1.7 x 10-4 M and 9.3 x 10-4 M, respectively) evidencing very different molecular structures and the greater cloud-forming efficiency of the surfactants from remote regions.
In a second study, the potential role of surfactants on cloud formation was explored by comparing the analysis of the surfactants in PM1 aerosols (237 samples) with cloud occurrence over 9 months (257 clouds) at the remote Pallas Supersite of the Finnish Meteorological Institute in Finland. Statistical analyses (Canonical Correlation Analysis, CCA, and regression analyses) were applied to the data and revealed strong co-dependencies between the surfactant properties (ratio of concentration over CMC, C/CMC, quantifying the surfactant efficiency) and cloud frequency. As no such co-dependency was found between the surfactants and any of the other cloud-relevant variables (temperature, relative humidity, aerosol particle radius, and hygroscopic composition) these results suggested a direct, physical connection between the surfactants properties in PM1 and cloud properties. This connection was further confirmed by time-dependent analyses showing that each increase in surfactant efficiency observed over a 48h-period coincided with an increase in cloud frequency. These results are the first atmospheric evidence for a causality relationship between surfactants in PM1 aerosols and cloud formation
The traditional voltammetric method at the mercury electrode, and an acidification step developed for the determination of reduced sulfur species (RSS) in natural waters, was for the first time used for the quantification of RSS in the water-soluble fraction of fine marine aerosols collected at the Middle Adriatic location (Rogoznica Lake). The evidence of two types of non-volatile RSS that have different interaction with the Hg electrode was confirmed: mercapto-type which complexes Hg as RS–Hg and sulfide/S0-like compounds which deposits HgS. The analytical protocol that was used for RSS determination in aerosol samples is based on separate voltammetric studies of a methyl 3-mercaptopropionate (3-MPA) as a representative of mercapto-type compounds and sulfide as a representative of inorganic RSS. Our preliminary study indicates the presence of mainly RS–Hg compounds in spring samples, ranging from 2.60–15.40 ng m−3, while both, the mercapto-type (0.48–2.23 ng m−3) and sulfide and/or S0-like compounds (0.02–0.26 ng m−3) were detected in early autumn samples. More expressed and defined RS–Hg peaks recorded in the spring potentially indicate their association with biological activity in the area. Those samples were also characterized by a higher water-soluble organic carbon content and a more abundant surface-active fraction, pointing to enhanced solubility and stabilization of RSS in the aqueous atmospheric phase.
Abstract The assimilation of inorganic nutrients by phytoplankton strongly depends on environmental conditions such as the availability of nitrogen and temperature, especially warming. The acclimation or adaptation of different species to such changes remains poorly understood. Here, we used a multimethod approach to study the viability and physiological and biochemical responses of the marine diatom Chaetoceros pseudocurvisetus to different temperatures (15, 25, and 30 °C) and different N:P ratios. Nitrogen limitation had a greater effect than high temperature on cell growth and reproduction, leading to a marked elongation of setae, decreased phosphorus assimilation, increased lipid accumulation, and decreased protein synthesis. The elongation of setae observed under these conditions may serve to increase the surface area available for the uptake of inorganic and/or organic nitrogen. In contrast, high temperatures (30 °C) had a stronger effect than nitrogen deficiency on cell death, nitrogen assimilation, chlorophyll a accumulation, the cessation of setae formation, and cell lipid remodelling. Significant changes in thylakoid lipids were observed in cells maintained at 30 °C, with increased levels of digalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol. These changes may be explained by the role of galactolipids in thylakoid membrane stabilization during heat stress.
<p>Nowadays, various environmental compartments are under increasing pressure from anthropogenic impact, and we as a society, have a duty, to understand the extent of the changing environment and how this may affect the functioning of global earth processes. More than 70% of the Earth&#8217;s surface is covered by the ocean whose uppermost layer, the sea surface microlayer (SML), is a specific environment at the air-sea interface, that is highly susceptible to increasing human impacts and climate change. SML has short- and long-term impacts on a range of planetary processes, including global biogeochemical cycling, air-sea exchange of gases and particles, and climate regulation. The SML is highly enriched in organic matter (OM) and has biofilm-like properties, and due to direct solar radiation, provides a challenging habitat for a wide variety of auto- and heterotrophic organisms. This makes SML a site of unique photochemical reactions that result in significant abiotic production of unsaturated and functionalized volatile organic compounds acting as precursors for the formation of marine secondary organic aerosols. The cycling of OM through the microbial food web at the sea surface determines the accumulation and enrichments of OM at SML, which directly affects the gas exchange rates and chemical composition of aerosols released from the sea surface to the atmosphere. Although the SML is involved in all ocean-atmosphere exchange processes, especially for climate-relevant gases and aerosol particles, its biogeochemical functioning during diurnal cycles is poorly characterized.</p><p>Therefore, in the summer of 2020, a multidisciplinary field campaign was conducted in the central Adriatic Sea, which included three full diurnal cycles of simultaneous sampling of the SML, with a special sampler, underlying water (ULW) and atmospheric aerosols (particulate matter < 10 &#181;m, PM<sub>10</sub>). The results of biochemical analyses of SML and ULW including dissolved (DOC) and particulate organic carbon (POC), nutrients (NO<sub>3</sub><sup>-</sup>, NH<sub>4</sub><sup>+</sup>, PO<sub>4</sub><sup>3-</sup>), lipids, transparent exopolymeric particles (TEP) and Coomassie stainable particles (CSP), surface active substances (SAS), phytoplankton and heterotrophic bacteria abundance as well as results of mass concentrations and total organic carbon (OC), water soluble organic carbon (WSOC), SAS and ions (Cl<sup>-</sup>, NO<sub>3</sub><sup>-</sup>, SO<sub>4</sub><sup>2-</sup>, Na<sup>+</sup>, NH<sub>4</sub><sup>+</sup>, K<sup>+</sup>, Mg<sup>2+</sup>, Ca<sup>2+</sup>) determined in PM<sub>10</sub> samples were correlated and statistically analysed depending on their solar radiation exposure. The comprehensive data-set will be discussed to investigate diurnal variations in the coupling between meteorological forcing, SML physicochemical and biological properties, and air&#8211;sea exchange of aerosol particles. This interdisciplinary diurnal study represents a promising approach in contributing to the fundamental current knowledge of ocean&#8211;atmosphere feedbacks, crucial for exploring global biogeochemical cycles, as well as predicting human impact on future climate changes.</p><p>Acknowledgment: This work has been supported by DAAD project &#8220;Diurnal dynamics on the sea-atmosphere interface" and Croatian Science Foundation under the IP-2018-01-3105 BiREADI project.</p>