Surface Microlayer Research Articles

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.

Hydrocarbons in the Surface Microlayer and Ice of the Kara Sea

Hydrocarbons in the Surface Microlayer and Ice of the Kara Sea

Atmospheric particle abundance and sea salt aerosol observations in the springtime Arctic: a focus on blowing snow and leads

Abstract. Sea salt aerosols play an important role in the radiation budget and atmospheric composition over the Arctic, where the climate is rapidly changing. Previous observational studies have shown that Arctic sea ice leads are an important source of sea salt aerosols, and modeling efforts have also proposed blowing snow sublimation as a source. In this study, size-resolved atmospheric particle number concentrations and chemical composition were measured at the Arctic coastal tundra site of Utqiaġvik, Alaska, during spring (3 April–7 May 2016). Blowing snow conditions were observed during 25 % of the 5-week study period and were overpredicted by a commonly used blowing snow parameterization based solely on wind speed and temperature. Throughout the study, open leads were present locally. During periods when blowing snow was observed, significant increases in the number concentrations of 0.01–0.06 µm particles (factor of 6, on average) and 0.06–0.3 µm particles (67 %, on average) and a significant decrease (82 %, on average) in 1–4 µm particles were observed compared to low wind speed periods. These size distribution changes were likely caused by the generation of ultrafine particles from leads and/or blowing snow, with scavenging of supermicron particles by blowing snow. At elevated wind speeds, both submicron and supermicron sodium and chloride mass concentrations were enhanced, consistent with wind-dependent local sea salt aerosol production. At moderate wind speeds below the threshold for blowing snow as well as during observed blowing snow, individual sea spray aerosol particles were measured. These individual salt particles were enriched in calcium relative to sodium in seawater due to the binding of this divalent cation with organic matter in the sea surface microlayer and subsequent enrichment during seawater bubble bursting. The chemical composition of the surface snowpack also showed contributions from sea spray aerosol deposition. Overall, these results show the contribution of sea spray aerosol production from leads on both aerosols and the surface snowpack. Therefore, if blowing snow sublimation contributed to the observed sea salt aerosol, the snow being sublimated would have been impacted by sea spray aerosol deposition rather than upward brine migration through the snowpack. Sea spray aerosol production from leads is expected to increase, with thinning and fracturing of sea ice in the rapidly warming Arctic.

Controls on the Distribution, Enrichment, and Degradation of Dissolved Organic Matter in the Sea Surface Microlayer of the Yellow Sea and East China Sea

AbstractThe concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), total dissolved carbohydrates (TDCHO), and total hydrolyzable amino acids (THAA) in the sea surface microlayer (SML) and subsurface water (SSW) were measured in the Yellow Sea and East China Sea. Concentrations of DOC and TDCHO in the SML were correlated with their respective concentrations in the SSW (Pearson's correlations: DOC, r2 = 0.17, n = 45, p &lt; 0.01; TDCHO, r2 = 0.32, n = 45, p &lt; 0.01). In contrast, DON and THAA concentrations in the SML and SSW were not correlated, suggesting that processes other than exchange with SSW dominated their loss or gain in the SML. Both THAA and TDCHO were significantly enriched in the SML, with mean enrichment factors (EFs) of 2.24 ± 1.17 and 1.98 ± 1.08, respectively. The EFs of dissolved organic matter (DOM) were not correlated with wind speed under the influence of complex processes (e.g., bubbling and turbulence). THAA‐C% and TDCHO‐C% in the SML were 3.38 ± 1.71% and 8.49 ± 4.81%, respectively, which were significantly higher than those in the SSW (Mann‐Whitney U test, p &lt; 0.05), suggesting that DOM in the SML was fresher than that in the SSW. While the high bioavailability of DOM in the SML should be conducive to neuston proliferation in this unique environment, no significant correlations were observed between degradation indicators and neuston abundances. In contrast, the changes of temperature and pH may have an important impact on the degradation of DOM.

Organic Signatures of Surfactants and Organic Molecules in Surface Microlayer and Subsurface Water of Delaware Bay

Organic Signatures of Surfactants and Organic Molecules in Surface Microlayer and Subsurface Water of Delaware Bay

Climate Disruption Caused by a Decline in Marine Biodiversity and Pollution

The world has focused on carbon mitigation as the only solution for climate change. This discussion paper considers how marine biodiversity regulates the climate, and the factors that control marine biodiversity.&#x0D; The main Greenhouse Gas (GHG) is water vapor, which accounts for 75% of all GHGs; the second most important is carbon dioxide, followed by methane and particulates such as black carbon (BC) soot. The concentration of water vapor in the atmosphere is regulated by air temperature; warmer conditions lead to higher evaporation, which in turn increases the concentration of water vapor, the Clausius-Clapeyron relation. This means that as the oceans and atmosphere warm, a self-reinforcing feedback loop accelerates the evaporation process to cause further warming.&#x0D; It is not considered possible to directly regulate atmospheric water vapor. This explains why climate change mitigation strategies have focussed primarily on reducing carbon dioxide emissions as the means to reduce water vapor. This report concludes that the current climate change mitigation strategy will not work on its own because it depends on decreasing the concentration of atmospheric carbon dioxide and on the assumption that water vapor is only regulated by temperature.&#x0D; 71% of planet Earth is covered by an ocean that has a surface microlayer (SML) between 1 µm and 1000µm deep, composed of lipids and surfactants produced by marine phytoplankton. This SML layer is known to promote the formation of aerosols and clouds; it also reduces the escape of water molecules and slows the transfer of thermal energy to the atmosphere. The concentration of water vapor is increasing in our atmosphere, and 100% of this increase is evaporation from the ocean surface; water vapour from land systems is decreasing. This means that the oceans are almost entirely responsible for climate change.&#x0D; The SML layer attracts toxic forever, lipophilic chemicals, microplastics and hydrophobic black carbon soot from the incomplete combustion of fossil fuels. Concentrations of toxic chemicals are 500 times higher in this SML layer than in the underlying water. Toxic forever chemicals combined with submicron and microplastic particles and black carbon particulates are known to be toxic to plankton. Marine primary productivity or phytoplankton photosynthesis may have declined by as much as 50% since the 1950s. Reduced phytoplankton plant growth equates to a degraded SML membrane, reduced carbon assimilation, and higher concentrations of dissolved carbon dioxide in ocean surface water, which accelerates the decline in ocean pH. The key phytoplankton species responsible for the production of the SML layer are the first to suffer from pH decline, a process called “ocean acidification”.&#x0D; Ocean acidification will lead to a regime shift away from the key carbonate-based species and diatoms below pH 7.95 which will be reached by 2045. The SML layer will decrease, allowing evaporation and atmospheric water vapor concentrations to increase. A reduced SML layer will lead to fewer aerosols, cloud formation and precipitation, as well as increased humidity and temperature. When clouds form under these conditions, the higher humidity will cause torrential downpours and flooding. The result could be catastrophic climate change, even if we achieve net zero by 2050. In parallel, ocean acidification and the collapse of the marine ecosystem could also lead to the loss of most seals, birds, whales, fish, and food supply for 3 billion people.

How biogenic polymers control surfactant dynamics in the surface microlayer: insights from a coastal Baltic Sea study

Abstract. Surfactants can hamper gas exchange by up to 50 % in coastal seas; however, their small-scale temporal and spatial dynamics are poorly constrained. This study investigated possible biogenic sources of surfactants in the sea surface microlayer (SML) and the underlying water at a coastal Baltic Sea site. To relate surfactant dynamics to biogenic production, we conducted two field studies (June and September 2018) and focused on amino acids and carbohydrates as the main components of organic matter derived from phytoplankton. Furthermore the composition of the biochemicals provided insights into microbial degradation dynamics and was complemented by flow-cytometry-based community analysis. In total, 76 samples were collected within an area of approximately 50 km2, allowing for high spatial resolution. Moreover, morning and afternoon sampling enabled us to investigate diel cycles. Our results reveal that surfactant concentrations were tightly coupled to the abundance of nano-phytoplankton and generally higher in September than in June, with cell abundance 3 times higher. Surfactant concentration in June was best explained by the combined effect of the particulate fraction of the non-essential amino acid serine, the concentration of particulate combined carbohydrates (PCHO), and dissolved organic carbon (DOC). Surfactant and PCHO concentrations were significantly enriched in the SML and followed a pronounced diel cycle, possibly linked to microbial processing and/or photo-processing. In contrast to June, the surfactant pool in September correlated to a diverse mixture of semi-labile organic matter components, represented best by dissolved glucose and the essential amino acid isoleucine. We conclude that the surfactant pool in surface seawater is mainly composed of organic matter components that resist rapid microbial degradation. Elevated surfactant concentrations are triggered by the release of fresh organic matter. While the effect of the resistant but less surface-active stock is potentially longer-lasting, the additive effect of labile, highly surface-active agents on gas exchange may diminish on short timescales.

Dimethyl sulfide cycling in the sea surface microlayer in the southwestern Pacific – Part 2: Processes and rates

Abstract. As the sea surface microlayer (SML) is the uppermost oceanic layer and differs in biogeochemical composition to the underlying subsurface water (SSW), it is important to determine whether processes in the SML modulate gas exchange, particularly for climate active gases. Enrichment of dimethyl sulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) has been reported in the SML, but it remains unclear how this is maintained whilst DMS is lost to the atmosphere. To examine this, a comprehensive study of DMS source and sink processes, including production, consumption, and net response to irradiance, was carried out in deck-board incubations of SML water at five locations in different water masses in the southwestern Pacific east of New Zealand. Net consumption of DMSP and production of DMS in the light and dark occurred at all sites. The net response of DMS and DMSP to irradiance varied between stations but was always lower than conversion of DMSP to DMS in the dark. In addition, DMS photolytic turnover was slower than reported elsewhere, which was unexpected given the high light exposure in the SML incubations. Although no relationships were apparent between DMS process rates and biogeochemical variables, including chlorophyll a, bacteria, and phytoplankton groups, net bacterial DMSP consumption was correlated with DMSP and DMS concentrations and also dinoflagellate and Gymnodinium spp. biomass, supporting the findings of a companion study that dinoflagellates play an important role in DMS cycling in the SML. However, net DMS production rates and accumulation were low relative to regional air–sea DMS loss, indicating that DMS cycling within the SML is unlikely to influence regional DMS emissions.

A Persistent Submesoscale Frontal Slick: A Novel Marker of the Mesoscale Flow Field in a Large Lake (Lake Geneva)

AbstractSubmesoscale fronts often become visible when the accumulation of biosurfactants in the water surface microlayer causes smooth surfaces, called frontal slicks, to develop. Based on in situ and remotely‐sensed data, a frontal slick was documented for the first time in a lake (Lake Geneva). A quasi‐stationary ∼10‐km long slick formed on the warm side of a surface temperature front with strong horizontal velocity strain. The slick width increased from ∼50 to ∼200 m in ∼1.5 hr due to “feeding” by wind‐driven, rapidly‐moving smaller slicks. Numerical modeling results, confirmed by satellite data, indicated that the boundary between mesoscale gyres isolated warm surface water from cold water associated with wind‐induced coastal upwelling. Measurements and modeling suggest that frontogenetic sharpening of the submesoscale temperature gradient created an active front with strong convergent flow. Such dynamics must be considered in buoyant material transport and the vertical exchange of surface water with deeper layers in lakes.

SURFACE MODIFICATION OF MACHINE PARTS AND MECHANISMS IN THE CONDITIONS OF FRICTION AND WEAR

The issues of surface modification of machine parts and mechanisms in conditions of friction and wear with and without oil further develops that work. The dependence of antifriction and friction on the special state of only the surface layers of friction parts is considered. It is revealed that the structural changes that occur in the surface microlayer of conjugate materials, the formation and destruction of secondary structures are responsible for the nature of the friction node. The authors propose to create on the friction surface such protective coatings that have properties and mechanism of action corresponding to secondary structures in order to be able to control the phenomena of antifriction and fractionality in the friction zone of conjugate parts. The aim of the study is achieved by processing iron-carbon alloys in the environment of superheated steam of aqueous solutions of salts. The optimal parameters of the technological process of forming coatings during vapor oxidation are selected. Laboratory tests of different chemical composition of the formed coating on the tribotechnical properties of friction steam were carried out. During the study, the authors concluded that by establishing a qualitative and quantitative relationship between the composition of oxide coatings and their tribotechnical properties, it is possible to change the conditions of the friction unit from antifriction to friction, using the same structural materials - ferrocarbon alloys. Thus, complex oxides, which differ in chemical composition and structure, which are coatings on ferrocarbon alloys, can significantly affect the thermomechanophysical processes that occur during operation and allow their renovation in the presence of lubricant and without it. Coatings formed on the surface of ferrocarbon alloys in accordance with the operating conditions can have both friction and antifriction properties.

Molecular Characterization of the Product Compounds Formed Upon Heterogeneous Chemistry of Ozone With Riverine Surface Microlayer

AbstractOzone (O3) is an important trace gas and oxidant in the atmosphere which sources and sinks are not well understood. In this study we measured the uptake coefficients of O3 (100 ppb) on authentic riverine surface microlayers (SML) collected on three different places on Pearl River in Guangzhou by a vertical wetted wall flow tube reactor which enables to estimate the deposition velocity of O3 on the fresh water surface. The product compounds formed upon interfacial reactions of O3 with the SML have been investigated by a Fourier transform ion cyclotron resonance mass spectrometry. About 10 times more product compounds were formed upon ozonolysis on the SML sample collected in a transportation hub close to the Estuary zone compared to the products formed upon ozonolysis on the SML sampled at the upper reach of the river at the periphery of Guangzhou. Moreover, 933 nitrogen (N)‐containing organic compounds which are associated with nitrooxy amines, organonitrates, nitroaromatics, and peroxyacetyl nitrates were formed upon heterogeneous reaction of ozone with the SML collected near the Estuary zone compared to 165 N‐containing compounds formed upon ozonolysis of the SML sample collected at the periphery of the city. Hence, the formed condensed phase product compounds through the reactions of ozone with the riverine SML can affect the freshwater biodiversity. An important fraction of brown carbon compounds was formed, which may be released to the air by wind‐wave interactions and influence the chemical composition of the atmosphere and thus, radiative forcing of the aerosols.

Metal complexation, FT-IR characterization, and plankton abundance in the marine surface microlayer of coastal areas in the Eastern Mediterranean

Barely any data exist on metal speciation in the marine surface microlayer (SML), a rather complex environment, the study of which contributes to enhancement of knowledge on metal speciation and its effect to the ocean. Metal speciation is significant since life requires a wide variety of trace metals that are essential for the growth of the organisms. Ligand concentrations (L) of copper (Cu), zinc (Zn), and cadmium (Cd) were studied by anodic stripping voltammetry (ASV) in the SML of coastal areas within the Aegean Sea in the Eastern Mediterranean. Complexing capacities in the SML in decreasing order ranged for Cu from 29 to 201 nM (median 101 nM), for Zn 24–149 nM (45 nM), and for Cd 1.0–1.5 nM (1.4 nM). Average enrichment factors (EFs) of SML samples compared to subsurface ones (SSW) were calculated equal to 0.9 ± 0.8, 1.2 ± 0.5, and 1.7 ± 1.6 for LZn, LCu, and LCd, respectively. In five out of the six total paired samples of SML and SSW, lower concentrations of LZn were measured in the SML, which is not the case for LCu and LCd. Due to elevated dissolved Zn concentrations in the SML, its complexation is incomplete, contrary to those of Cu and Cd, which are fully complexed. These trace metals are essential nutrients for biological functions, hence any differences on their concentration and chemical speciation may directly influence the distribution of phytoplankton species in the upper water column and neuston. EFs of SML relatively to subsurface water ranged in average between 1.2 and 2.4 for total organic carbon (TOC), chlorophyll a (Chla), and plankton, being generally &amp;gt;2 for most of the amino acids detected, demonstrating a relative enrichment of the SML in organic matter. A significant correlation was found between Cu ligands and dinoflagellates &amp;lt;20 μm, confirming older findings supporting that marine dinoflagellates of Gymnodinium genera produce Cu ligands. New insights are provided in the study and the importance of investigating bio-essential metal ions (Cu, Zn, Cd) and their organic complexes in the SML is pointed. Data on Zn and Cd complexing capacities in the SML are the first published so far.

Enrichment of poly- and perfluoroalkyl substances (PFAS) in the surface microlayer and foam in synthetic and natural waters

Bench-scale experiments were performed to interrogate poly- and perfluoroalkyl substance (PFAS) enrichment in the water surface microlayer (SML). In initial experiments using electrolyte-only solutions, the perfluorooctane sulfonate (PFOS) and perfluorooctane carboxylate (PFOA) enrichment in the SML were reasonably (with a factor of 2) described by the Gibbs adsorption equation coupled with a Freundlich-based interfacial adsorption model. Enrichment in the SML among perfluorinated sulfonates and perfluorinated carboxylates of varying chain lengths was proportional to their surface activity. The PFOS enrichment factor (EF), defined as the PFAS concentration in the SML divided by the concentration in the bulk water, was 18 in a 200 mg/l NaCl solution. The presence of elevated organic carbon levels in synthetic surface waters inhibited PFAS accumulation in the SML, with resulting EF values of approximately 1 for all PFAS. However, in the presence of elevated organic levels coupled with foam, PFAS enrichment in the foam was observed, with a foam EF of 25 measured for PFOS in synthetic surface waters. PFAS EF values measured in several natural surface waters without foam showed little variation among the waters tested, with PFOS EF values ranging between 6 and 10. Together, these results suggest that PFAS accumulation in the SML is largely controlled by PFAS sorption at the air-water interface for the conditions examined in this study, and the presence of foam with natural organics enhances PFAS uptake at the water surface.

210Pb and 7Be as Coupled Flux and Source Tracers for Aerosols in the Pacific Ocean

AbstractDeposition of aerosols to the surface ocean is an important factor affecting primary production in the surface ocean. However, the sources and fluxes of aerosols and associated trace elements remain poorly defined. Aerosol 210Pb, 210Po, and 7Be data were collected on US GEOTRACES cruise GP15 (Pacific Meridional Transect, 152°W; 2018). 210Pb fluxes are low close to the Alaskan margin, increase to a maximum at ∼43°N, then decrease to lower values. There is good agreement between 210Pb fluxes and long‐term land‐based fluxes during the SEAREX program (1970–1980s), as well as between GP15 and GP16 (East Pacific Zonal Transect, 12°S; 2013) at adjacent stations. A normalized fraction f(7Be, 210Pb) is used to discern aerosols with upper (high f) versus lower (low f) troposphere sources. Alaskan/North Pacific aerosols show significant continental influence while equatorial/South Pacific aerosols are supplied to the marine boundary layer from the upper troposphere. Lithogenic trace elements Al and Ti show inverse correlations with f(7Be, 210Pb), supporting a continental boundary layer provenance while anthropogenic Pb shows no clear relationship with f(7Be, 210Pb). All but four samples have 210Po/210Pb activity ratios &lt;0.2 suggesting short aerosol residence time. Among the four samples (210Po/210Pb = 0.42–0.88), two suggest an upper troposphere source and longer aerosol residence time while the remaining two cannot be explained by long aerosol residence time nor a significant component of dust. We hypothesize that enrichments of 210Po in them are linked to Po enrichments in the sea surface microlayer, possibly through Po speciation as a dissolved organic or dimethyl polonide species.

Does Sea Spray Aerosol Contribute Significantly to Aerosol Trace Element Loading? A Case Study From the U.S. GEOTRACES Pacific Meridional Transect (GP15)

AbstractAtmospheric deposition represents a major input for micronutrient trace elements (TEs) to the surface ocean and is often quantified indirectly through measurements of aerosol TE concentrations. Sea spray aerosol (SSA) dominates aerosol mass concentration over much of the global ocean, but few studies have assessed its contribution to aerosol TE loading, which could result in overestimates of “new” TE inputs. Low‐mineral aerosol concentrations measured during the U.S. GEOTRACES Pacific Meridional Transect (GP15; 152°W, 56°N to 20°S), along with concurrent towfish sampling of surface seawater, provided an opportunity to investigate this aspect of TE biogeochemical cycling. Central Pacific Ocean surface seawater Al, V, Mn, Fe, Co, Ni, Cu, Zn, and Pb concentrations were combined with aerosol Na data to calculate a “recycled” SSA contribution to aerosol TE loading. Only vanadium was calculated to have a SSA contribution averaging &gt;1% along the transect (mean of 1.5%). We derive scaling factors from previous studies on TE enrichments in the sea surface microlayer and in freshly produced SSA to assess the broader potential for SSA contributions to aerosol TE loading. Maximum applied scaling factors suggest that SSA could contribute significantly to the aerosol loading of some elements (notably V, Cu, and Pb), while for others (e.g., Fe and Al), SSA contributions largely remained &lt;1%. Our study highlights that a lack of focused measurements of TEs in SSA limits our ability to quantify this component of marine aerosol loading and the associated potential for overestimating new TE inputs from atmospheric deposition.

Surface and Subsurface Properties of Aquatic Ecosystems

The surface microlayer (SML) is the dividing border between the air and water surface. It has physical, chemical and biological properties which are distinctly from subsurface layer (SSL) waters. As its unique place between the air- water, the SML has remained in a distinct research corner. Surface microlayer is characterized by the capacity to accumulate of organic chemical compounds specially proteins, carbohydrates and lipid. The presence of such as energy-rich organic matters in the surface microlayer creates distinct condition for the accumulation and development of aerobic bacteria mainly heterotrophic bacteria forming bacterio-neuston

Effects of natural surfactants on the spatial variability of surface water temperature under intermittent light winds on Lake Geneva

The spatial variability of lake surface water temperature (LSWT) between smooth and rough surface areas and its potential association with the natural surfactant distribution in the surface microlayer were investigated for the first time in a lake. In spring 2019, two different field campaigns were carried out in Lake Geneva to measure: i) the enrichment factor of fluorescent dissolved organic matter (FDOM) as a proxy for biogenic surfactants, and ii) LSWT and near-surface water temperature profiles while simultaneously monitoring water surface roughness in both cases. Results indicate that, under intense incoming short-wave radiation and intermittent light wind conditions, the atmospheric boundary layer (ABL) was stable and the accumulation of heat due to short-wave radiation in near-surface waters was greater than heat losses by surface cooling, thus creating a diurnal warm layer with strong thermal stratification in the water near-surface layer. A threshold wind speed of 1.5 m s-1 was determined as a transition between different dynamic regimes. For winds just above 1.5 m s-1, the lake surface became patchy, and smooth surface areas (slicks) were more enriched with FDOM than rough areas (non-slick) covered with gravity-capillary waves (GCW). Sharp thermal boundaries appeared between smooth and rough areas. LSWT in smooth slicks was found to be more than 1.5°C warmer than in rough non-slick areas, which differs from previous observations in oceans that reported a slight temperature reduction inside slicks. Upon the formation of GCW in non-slick areas, the near-surface stratification was destroyed and the surface temperature was reduced. Furthermore, winds above 1.5 m s-1 continuously fragmented slicks causing a rapid spatial redistribution of LSWT patterns mainly aligned with the wind. For wind speeds below 1.5 m s‑1 the surface was smooth, no well-developed GCW were observed, LSWT differences were small, and strong near-surface stratification was established. These results contribute to the understanding and the quantification of air-water exchange processes, which are presently lacking for stable Atmospheric Boundary Layer conditions in lakes.

Isotopic Insights into Organic Composition Differences between Supermicron and Submicron Sea Spray Aerosol.

To elucidate the seawater biological and physicochemical factors driving differences in organic composition between supermicron and submicron sea spray aerosol (SSAsuper and SSAsub), carbon isotopic composition (δ13C) measurements were performed on size-segregated, nascent SSA collected during a phytoplankton bloom mesocosm experiment. The δ13C measurements indicate that SSAsuper contains a mixture of particulate and dissolved organic material in the bulk seawater. After phytoplankton growth, a greater amount of freshly produced carbon was observed in SSAsuper with the proportional contribution being modulated by bacterial activity, emphasizing the importance of the microbial loop in controlling the organic composition of SSAsuper. Conversely, SSAsub exhibited no apparent relationship with biological activity but tracked closely with surface tension measurements probing the topmost ∼0.2-1.5 μm of the sea surface microlayer. This probing depth is similar to a bubble's film thickness at the ocean surface, suggesting that SSAsub organic composition may be influenced by the presence of surfactants at the air-sea interface that are transferred into SSAsub by bubble bursting. Our findings illustrate the substantial impact of seawater dynamics on the pronounced organic compositional differences between SSAsuper and SSAsub and demonstrate that these two SSA populations should be considered separately when assessing their contribution to marine aerosols and climate.

Characterization of Sea Surface Microlayer and Marine Aerosol Organic Composition Using STXM-NEXAFS Microscopy and FTIR Spectroscopy

Characterization of Sea Surface Microlayer and Marine Aerosol Organic Composition Using STXM-NEXAFS Microscopy and FTIR Spectroscopy

Distribution and characterization of organic matter within the sea surface microlayer in the Gulf of Gdańsk

We present the characterisation and distribution of organic matter (OM) within the sea surface microlayer (SML) and underlying water (ULW) collected in October 2015 at nine stations in the Baltic Sea, Gulf of Gdańsk, encompassing the Vistula River plume. The salinity of >7 throughout the transect indicated Vistula plume was possibly displaced westward by the preceding northerly and easterly winds between 5.7 and 10.7 ms–1 during the sampling campaign. Spectral analysis pointed to the highest contribution of aromatic and high molecular weight molecules (lowest spectral slope (SR) ratios and highest absorption coefficient at 254 nm (aCDOM(254)) at the first two stations near the river mouth, demonstrating a very limited influence of the river plume. Concentrations of surface-active organic substances (SAS) ranged from 0.28 to 0.60 mg L−1 in eq. Triton-X-100 in SML, and from 0.22 to 0.47 mg L−1 in eq. Triton-X-100 in the ULW, while POC concentrations ranged from 0.27 to 0.84 mg L−1 in SML and from 0.20 to 0.37 mg L−1 in ULW. Enrichment of SAS and POC detected at the highest wind speeds indicates rapid SML recovery by OM transported from the ULW. Low lipids to POC contribution, on average 5% and 7% in SML and ULW respectively, points to eutrophic conditions. Statistically significant negative correlation between SR and the Lipid:PIG ratio in SML and ULW suggests the production of lower molecular weight OM by phytoplankton living under favourable environmental conditions. Accumulation of lipid reserves triacylglycerols (TG) in the SML indicates more stressful plankton growth conditions compared to ULW.