Sea Surface Microlayer Research Articles

Concerted measurements of lipids in seawater and on submicrometer aerosol particles at the Cabo Verde islands: biogenic sources, selective transfer and high enrichments

Abstract. In the marine environment, measurements of lipids as representative species within different lipid classes have been performed to characterize their oceanic sources and their transfer from the ocean into the atmosphere to marine aerosol particles. The set of lipid classes includes hydrocarbons (HC); fatty acid methyl esters (ME); free fatty acids (FFA); alcohols (ALC); 1,3-diacylglycerols (1,3 DG); 1,2-diacylglycerols (1,2 DG); monoacylglycerols (MG); wax esters (WE); triacylglycerols (TG); and phospholipids (PP) including phosphatidylglycerols (PG), phosphatidylethanolamine (PE), phosphatidylcholines (PC), as well as glycolipids (GL) which cover sulfoquinovosyldiacylglycerols (SQDG), monogalactosyl-diacylglycerols (MGDG), digalactosyldiacylglycerols (DGDG) and sterols (ST). These introduced lipid classes have been analyzed in the dissolved and particulate fraction of seawater, differentiating between underlying water (ULW) and the sea surface microlayer (SML) on the one hand. On the other hand, they have been examined on ambient submicrometer aerosol particle samples (PM1) which were collected at the Cape Verde Atmospheric Observatory (CVAO) by applying concerted measurements. These different lipids are found in all marine compartments but in different compositions. Along the campaign, certain variabilities are observed for the concentration of dissolved (∑DLULW: 39.8–128.5 µg L−1, ∑DLSML: 55.7–121.5 µg L−1) and particulate (∑PLULW: 36.4–93.5 µg L−1, ∑PLSML: 61.0–118.1 µg L−1) lipids in the seawater of the tropical North Atlantic Ocean. Only slight SML enrichments are observed for the lipids with an enrichment factor EFSML of 1.1–1.4 (DL) and 1.0–1.7 (PL). On PM1 aerosol particles, a total lipid concentration between 75.2–219.5 ng m−3 (averaged: 119.9 ng m−3) is measured. As also bacteria – besides phytoplankton sources – influence the lipid concentrations in seawater and on the aerosol particles, the lipid abundance cannot be exclusively explained by the phytoplankton tracer (chlorophyll a). The concentration and enrichment of lipids in the SML are not related to physicochemical properties which describe the surface activity. On the aerosol particles, an EFaer (the enrichment factor on the submicrometer aerosol particles compared to the SML) between 9×104–7×105 is observed. Regarding the individual lipid groups on the aerosol particles, a statistically significant correlation (R2=0.45, p=0.028) was found between EFaer and lipophilicity (expressed by the KOW value), which was not present for the SML. But simple physicochemical descriptors are overall not sufficient to fully explain the transfer of lipids. As our findings show that additional processes such as formation and degradation influence the ocean–atmosphere transfer of both OM in general and of lipids in particular, they have to be considered in OM transfer models. Moreover, our data suggest that the extent of the enrichment of the lipid class constituents on the aerosol particles might be related to the distribution of the lipid within the bubble–air–water interface. The lipids TG and ALC which are preferably arranged within the bubble interface are transferred to the aerosol particles to the highest extent. Finally, the connection between ice nucleation particles (INPs) in seawater, which are already active at higher temperatures (−10 to −15 ∘C), and the lipid classes PE and FFA suggests that lipids formed in the ocean have the potential to contribute to (biogenic) INP activity when transferred into the atmosphere.

Experimental evidence of plastic particles transfer at the water-air interface through bubble bursting.

Plastic debris in the marine environment are the subject of an extensive literature. According to studies dedicated to the determination of plastic litter abundance and to the characterisation of degradation and fragmentation processes, models were used to estimate the global plastic debris abundance and to simulate their transfer and distribution. Despite these efforts, there is still missing plastic in the models used as areas exist where plastic abundance is less than that estimated. In parallel, microplastics presence in the atmosphere and in remote areas was confirmed suggesting long range atmospheric transport. Potentially addressing both these issues, recent literature suggests that microplastics (MPs) and nanoplastics (NPs) can be transferred from the marine environment to the atmosphere via the bursting of air bubbles at the sea surface. Nevertheless, to date there is no direct evidence of this transfer. In this study, we evaluate plastic particles transfer as a function of MPs/NPs characteristics and water composition by simulating the bubble bursting phenomenon in a laboratory reactor. Size distribution of transferred particles were recorded, and their plastic nature was confirmed using electron microscopy. Results show that under tested conditions, the transfer is possible but limited to particles smaller than 1μm. The influence of the presence of proxies of components of the sea surface microlayer in the water was evaluated showing a higher particle transfer rate in the presence of a surfactant (sodium dodecyl sulfate) and no significant effect of polysaccharides (xanthan gum and dextran). The surface state of the particles can alter their behaviour in the aqueous phase and thus their transfer to the atmosphere. The effect of bubble size was also evaluated showing a higher transfer rate with the smaller bubble size. In addition, experiments performed with grounded polyethylene (PE) samples showed higher transfer for UV-aged PE than for pristine PE.

Sea foams are ephemeral hotspots for distinctive bacterial communities contrasting sea-surface microlayer and underlying surface water.

ABSTRACTThe occurrence of foams at oceans’ surfaces is patchy and generally short-lived, but a detailed understanding of bacterial communities inhabiting sea foams is lacking. Here, we investigated how marine foams differ from the sea-surface microlayer (SML), a <1-mm-thick layer at the air–sea interface, and underlying water from 1 m depth. Samples of sea foams, SML and underlying water collected from the North Sea and Timor Sea indicated that foams were often characterized by a high abundance of small eukaryotic phototrophic and prokaryotic cells as well as a high concentration of surface-active substances (SAS). Amplicon sequencing of 16S rRNA (gene) revealed distinctive foam bacterial communities compared with SML and underlying water, with high abundance of Gammaproteobacteria. Typical SML dwellers such as Pseudoalteromonas and Vibrio were highly abundant, active foam inhabitants and thus might enhance foam formation and stability by producing SAS. Despite a clear difference in the overall bacterial community composition between foam and SML, the presence of SML bacteria in foams supports the previous assumption that foam is strongly influenced by the SML. We conclude that active and abundant bacteria from interfacial habitats potentially contribute to foam formation and stability, carbon cycling and air–sea exchange processes in the ocean.

Surface Tension Measurements of Aqueous Liquid-Air Interfaces Probed with Microscopic Indentation.

To elucidate the intricate role that the sea surface microlayer (SML) and sea spray aerosols (SSAs) play in climate, understanding the chemical complexity of the SML and how it affects the physical-chemical properties of the microlayer and SSA are important to investigate. While the surface tension of the SML has been studied previously using conventional experimental tools, accurate measurements must be localized to the thickness of the air-liquid interface of the SML. Here we explore the atomic force microscopy (AFM) capabilities to quantify the surface tension of aqueous solution droplets with (sub)micrometer indentation depths into the interface. Sample droplets of hexanoic acid at molar concentrations ranging from 0.1 to 80 mM and SML from a recent wave flume study were investigated. A constant-radius AFM nanoneedle was used to probe ca. 200 μL droplets with 0.3-1.2 μm indentation depths. As a comparison, the surface tension of bulk samples was also measured using a conventional force tensiometer. The data for the hexanoic acid show an excellent overlap between the AFM and force tensiometer surface tension measurements. For the surface tension measurements of the SML, however, the measured values from the AFM were 2.5 mN/m lower than that from the force tensiometer, which was attributed to the structural and chemical complexity of the SML, differences in the probing depth for each method, and the time scale required for the surface film to restructure as the needle is retracted away from the liquid surface. Overall, the study confirmed the accuracy of the AFM method in quantifying the surface tension of aqueous solutions over a wide range of concentrations for surface-active organic compounds. The methodology can be further used to reveal small, yet important, differences in the surface tension of complex air-liquid interfaces such as liquid systems where the type and concentration of surfactants vary with the distance from the air-liquid interface. For such complex systems, AFM measurements of the surface tension as a function of the probing depth and pulling rate may reveal a sublayer film structure of the liquid interface.

Prokaryotic abundance, cell size and extracellular enzymatic activity in a human impacted and mangrove dominated tropical estuary (Can Gio, Vietnam)

Extracellular enzymatic activities constitute the first and limiting step of the whole process of organic matter (OM) cycling in aquatic ecosystems. This study aims to identify the factors controlling prokaryotes ability to hydrolyse OM in an Indo-Pacific tropical mangrove ecosystem (Can Gio, Vietnam). Prokaryotic abundance and leucine-aminopeptidase exo-proteolytic activity (EPA) were measured at vertical (from the sea-surface microlayer to bottom waters), spatial (along a transect within the estuary) and seasonal (wet and dry season) scales. Prokaryotic abundance ranged from 1.2 to 5.7 × 109 cells L−1 and EPA ranged from 24 to 505 nmol L−1 h−1 that was relatively similar to other highly productive ecosystems. The estuary was poorly stratified, most probably because of high water turbulence. Yet, exo-proteolytic activity was significantly higher in bottom waters, where higher loads of suspended particulate matter were measured. Seasonal and spatial differences in EPA suggest that the nature of OM transported by the Can Gio mangrove estuary affect EPA. The latter seems to be increased by two “uncommon” situations: the input of fresh and labile OM (e.g. shrimp farm effluents) or the lack of labile OM and the need to hydrolyse refractory compounds (e.g. during the dry season).

Role of Sea Surface Microlayer Properties in Cloud Formation

To date, the relative contribution of primary marine organic matter to the subset of atmospheric particles that nucleate cloud droplets is highly uncertain. Here, cloud condensation nuclei (CCN) measurements were conducted on aerosolized sea surface microlayer (SML) samples collected from the North Atlantic Ocean during the NASA North Atlantic Aerosols and Marine Ecosystems Study (NAAMES), κ values were predicted for three representative high molecular weight (HMW) organic components of marine aerosol: 6-glucose, humic acid, and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). The predicted κ values for pure organic aerosols varied by only ±0.01 across all of the organics chosen. For the desalted SML samples, calculations assuming an organic composition of entirely RuBisCO provided the closest predicted κ values for the desalted SML samples with a mean κ value of 0.53 ± 0.10. These results indicate that it is the sea salt in the SML which drives the cloud formation potential of marine aerosols. While the presence of organic material from the ocean surface waters may increase aerosol mass due to enrichment processes, cloud formation potential of mixed organic/salt primary marine aerosols will be slightly weakened or unchanged compared to sea spray aerosol.

Concerted measurements of free amino acids at the Cabo Verde islands: high enrichments in submicron sea spray aerosol particles and cloud droplets

Abstract. Measurements of free amino acids (FAAs) in the marine environment to elucidate their transfer from the ocean into the atmosphere, to marine aerosol particles and to clouds, were performed at the MarParCloud (marine biological production, organic aerosol particles and marine clouds: a process chain) campaign at the Cabo Verde islands in autumn 2017. According to physical and chemical specifications such as the behavior of air masses, particulate MSA concentrations and MSA∕sulfate ratios, as well as particulate mass concentrations of dust tracers, aerosol particles predominantly of marine origin with low to medium dust influences were observed. FAAs were investigated in different compartments: they were examined in two types of seawater underlying water (ULW) and in the sea surface microlayer (SML), as well as in ambient marine size-segregated aerosol particle samples at two heights (ground height based at the Cape Verde Atmospheric Observatory, CVAO, and at 744 m height on Mt. Verde) and in cloud water using concerted measurements. The ∑FAA concentration in the SML varied between 0.13 and 3.64 µmol L−1, whereas it was between 0.01 and 1.10 µmol L−1 in the ULW; also, a strong enrichment of ∑FAA (EFSML: 1.1–298.4, average of 57.2) was found in the SML. In the submicron (0.05–1.2 µm) aerosol particles at the CVAO, the composition of FAAs was more complex, and higher atmospheric concentrations of ∑FAA (up to 6.3 ng m−3) compared to the supermicron (1.2–10 µm) aerosol particles (maximum of 0.5 ng m−3) were observed. The total ∑FAA concentration (PM10) was between 1.8 and 6.8 ng m−3 and tended to increase during the campaign. Averaged ∑FAA concentrations in the aerosol particles on Mt. Verde were lower (submicron: 1.5 ng m−3; supermicron: 1.2 ng m−3) compared to the CVAO. A similar contribution percentage of ∑FAA to dissolved organic carbon (DOC) in the seawater (up to 7.6 %) and to water-soluble organic carbon (WSOC) in the submicron aerosol particles (up to 5.3 %) indicated a related transfer process of FAAs and DOC in the marine environment. Considering solely ocean–atmosphere transfer and neglecting atmospheric processing, high FAA enrichment factors were found in both aerosol particles in the submicron range (EFaer(∑FAA): 2×103–6×103) and medium enrichment factors in the supermicron range (EFaer(∑FAA): 1×101–3×101). In addition, indications for a biogenic FAA formation were observed. Furthermore, one striking finding was the high and varying FAA cloud water concentration (11.2–489.9 ng m−3), as well as enrichments (EFCW: 4×103 and 1×104 compared to the SML and ULW, respectively), which were reported here for the first time. The abundance of inorganic marine tracers (sodium, methanesulfonic acid) in cloud water suggests an influence of oceanic sources on marine clouds. Finally, the varying composition of the FAAs in the different matrices shows that their abundance and ocean–atmosphere transfer are influenced by additional biotic and abiotic formation and degradation processes. Simple physicochemical parameters (e.g., surface activity) are not sufficient to describe the concentration and enrichments of the FAAs in the marine environment. For a precise representation in organic matter (OM) transfer models, further studies are needed to unravel their drivers and understand their composition.

Calcium bridging drives polysaccharide co-adsorption to a proxy sea surface microlayer.

Saccharides comprise a significant mass fraction of organic carbon in sea spray aerosol (SSA), but the mechanisms through which saccharides are transferred from seawater to the ocean surface and eventually into SSA are unclear. It is hypothesized that saccharides cooperatively adsorb to other insoluble organic matter at the air/sea interface, known as the sea surface microlayer (SSML). Using a combination of surface-sensitive infrared reflection-absorption spectroscopy and all-atom molecular dynamics simulations, we demonstrate that the marine-relevant, anionic polysaccharide alginate co-adsorbs to an insoluble palmitic acid monolayer via divalent cationic bridging interactions. Ca2+ induces the greatest extent of alginate co-adsorption to the monolayer, evidenced by the ∼30% increase in surface coverage, whereas Mg2+ only facilitates one-third the extent of co-adsorption at seawater-relevant cation concentrations due to its strong hydration propensity. Na+ cations alone do not facilitate alginate co-adsorption, and palmitic acid protonation hinders the formation of divalent cationic bridges between the palmitate and alginate carboxylate moieties. Alginate co-adsorption is largely confined to the interfacial region beneath the monolayer headgroups, so surface pressure, and thus monolayer surface coverage, only changes the amount of alginate co-adsorption by less than 5%. Our results provide physical and molecular characterization of a potentially significant polysaccharide enrichment mechanism within the SSML.

Extracellular enzyme activity under subzero hypersaline conditions by model cold-adapted bacteria and Arctic sea-ice microbial communities

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 87:99-111 (2021) - DOI: https://doi.org/10.3354/ame01974 Extracellular enzyme activity of model cold-adapted bacteria and Arctic sea-ice microbial communities under subzero hypersaline conditions G. M. Showalter*, J. W. Deming School of Oceanography and Astrobiology Program, University of Washington, Seattle, WA 98195, USA *Corresponding author: gmshowalter@gmail.com ABSTRACT: Bacterially produced extracellular enzymes (EEs) play an important role in the cycling of organic matter in the marine environment, breaking down large compounds to those small enough to be transported across the cell membrane. EEs may play an especially important role within the brines of sea ice, as freezing concentrates both bacteria and organic materials into brine pockets, leading to higher encounter rates between EEs and their substrates. However, whether EEs are able to perform under the extreme conditions of sea-ice brines, particularly during winter, is unknown. Here, we characterized EE activity (EEA) of leucine aminopeptidase produced by the psychrophilic bacterium Colwellia psychrerythraea strain 34H and the cold-tolerant Psychrobacter strain 7E, under analogue sea-ice conditions using a standard fluorescence-based activity assay. EEs produced by the psychrophile were active at the most extreme conditions tested, i.e. temperature of -8°C and salt concentration of 120 ppt, with activity enhanced if the EEs concerned were produced under subzero hypersaline conditions. EEs produced by the Psychrobacter strain were less cold- and salt-active. When high-latitude Arctic samples of sea-ice brine, under-ice water, and the sea-surface microlayer were analyzed using the same assay after a freeze-thaw cycle, EEA was highest in the sea-ice samples, with activity at -10°C and salinity of 142 ppt. Overall, these results indicate that EEA can contribute to the degradation of organic material in sea ice through winter, likely sustaining microbial communities in brine pores in the process and altering the nature of organic material released at spring melt. KEY WORDS: Arctic marine environment · Carbon cycle · Colwellia psychrerythraea strain 34H · Enzymatic activity · Psychrophiles · Sea ice · Psychrobacter strain 7E Full text in pdf format PreviousNextCite this article as: Showalter GM, Deming JW (2021) Extracellular enzyme activity of model cold-adapted bacteria and Arctic sea-ice microbial communities under subzero hypersaline conditions. Aquat Microb Ecol 87:99-111. https://doi.org/10.3354/ame01974 Export citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in AME Vol. 87. Online publication date: August 26, 2021 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2021 Inter-Research.

Overlooked Diversity of Ultramicrobacterial Minorities at the Air-Sea Interface

Members of the Candidate phylum Patescibacteria, also called Candidate Phyla Radiation (CPR), are described as ultramicrobacteria with limited metabolic capacities. Wide diversity and relative abundances up to 80% in anaerobic habitats, e.g., in groundwater or sediments are characteristic for Candidatus Patescibacteria. However, only few studies exist for marine surface water. Here, we report the presence of 40 patescibacterial candidate clades at air-sea interfaces, including the upper water layer, floating foams and the sea-surface microlayer (SML), a &lt; 1 mm layer at the boundary between ocean and atmosphere. Particle-associated (&gt;3 µm) and free-living (3–0.2 µm) samples were obtained from the Jade Bay, North Sea, and 16S rRNA (gene) amplicons were analyzed. Although the abundance of Cand. Patescibacteria representatives were relatively low (&lt;1.3%), members of Cand. Kaiserbacteria and Cand. Gracilibacteria were found in all samples. This suggests profound aerotolerant capacities of these phylogenetic lineages at the air-sea interface. The presence of ultramicrobacteria in the &gt;3 µm fraction implies adhesion to bigger aggregates, potentially in anoxic niches, and a symbiotic lifestyle. Due to their small sizes, Cand. Patescibacteria likely become aerosolized to the atmosphere and dispersed to land with possible implications for affecting microbial communities and associated processes in these ecosystems.

The ice-nucleating activity of Arctic sea surface microlayer samples and marine algal cultures

Abstract. In recent years, sea spray as well as the biological material it contains has received increased attention as a source of ice-nucleating particles (INPs). Such INPs may play a role in remote marine regions, where other sources of INPs are scarce or absent. In the Arctic, these INPs can influence water–ice partitioning in low-level clouds and thereby the cloud lifetime, with consequences for the surface energy budget, sea ice formation and melt, and climate. Marine aerosol is of a diverse nature, so identifying sources of INPs is challenging. One fraction of marine bioaerosol (phytoplankton and their exudates) has been a particular focus of marine INP research. In our study we attempt to address three main questions. Firstly, we compare the ice-nucleating ability of two common phytoplankton species with Arctic seawater microlayer samples using the same instrumentation to see if these phytoplankton species produce ice-nucleating material with sufficient activity to account for the ice nucleation observed in Arctic microlayer samples. We present the first measurements of the ice-nucleating ability of two predominant phytoplankton species: Melosira arctica, a common Arctic diatom species, and Skeletonema marinoi, a ubiquitous diatom species across oceans worldwide. To determine the potential effect of nutrient conditions and characteristics of the algal culture, such as the amount of organic carbon associated with algal cells, on the ice nucleation activity, Skeletonema marinoi was grown under different nutrient regimes. From comparison of the ice nucleation data of the algal cultures to those obtained from a range of sea surface microlayer (SML) samples obtained during three different field expeditions to the Arctic (ACCACIA, NETCARE, and ASCOS), we found that they were not as ice active as the investigated microlayer samples, although these diatoms do produce ice-nucleating material. Secondly, to improve our understanding of local Arctic marine sources as atmospheric INPs we applied two aerosolization techniques to analyse the ice-nucleating ability of aerosolized microlayer and algal samples. The aerosols were generated either by direct nebulization of the undiluted bulk solutions or by the addition of the samples to a sea spray simulation chamber filled with artificial seawater. The latter method generates aerosol particles using a plunging jet to mimic the process of oceanic wave breaking. We observed that the aerosols produced using this approach can be ice active, indicating that the ice-nucleating material in seawater can indeed transfer to the aerosol phase. Thirdly, we attempted to measure ice nucleation activity across the entire temperature range relevant for mixed-phase clouds using a suite of ice nucleation measurement techniques – an expansion cloud chamber, a continuous-flow diffusion chamber, and a cold stage. In order to compare the measurements made using the different instruments, we have normalized the data in relation to the mass of salt present in the nascent sea spray aerosol. At temperatures above 248 K some of the SML samples were very effective at nucleating ice, but there was substantial variability between the different samples. In contrast, there was much less variability between samples below 248 K. We discuss our results in the context of aerosol–cloud interactions in the Arctic with a focus on furthering our understanding of which INP types may be important in the Arctic atmosphere.

Influence of Arctic Microlayers and Algal Cultures on Sea Spray Hygroscopicity and the Possible Implications for Mixed‐Phase Clouds

AbstractAs Arctic sea ice cover diminishes, sea spray aerosols (SSA) have a larger potential to be emitted into the Arctic atmosphere. Emitted SSA can contain organic material, but how it affects the ability of particles to act as cloud condensation nuclei (CCN) is still not well understood. Here we measure the CCN‐derived hygroscopicity of three different types of aerosol particles: (1) Sea salt aerosols made from artificial seawater, (2) aerosol generated from artificial seawater spiked with diatom species cultured in the laboratory, and (3) aerosols made from samples of sea surface microlayer (SML) collected during field campaigns in the North Atlantic and Arctic Ocean. Samples are aerosolized using a sea spray simulation tank (plunging jet) or an atomizer. We show that SSA containing diatom and microlayer exhibit similar CCN activity to inorganic sea salt with a κ value of ∼1.0. Large‐eddy simulation (LES) is then used to evaluate the general role of aerosol hygroscopicity in governing mixed‐phase low‐level cloud properties in the high Arctic. For accumulation mode aerosol, the simulated mixed‐phase cloud properties do not depend strongly on κ, unless the values are lower than 0.4. For Aitken mode aerosol, the hygroscopicity is more important; the particles can sustain the cloud if the hygroscopicity is equal to or higher than 0.4, but not otherwise. The experimental and model results combined suggest that the internal mixing of biogenic organic components in SSA does not have a substantial impact on the cloud droplet activation process and the cloud lifetime in Arctic mixed‐phase clouds.

Influence of the Sea Surface Microlayer on Oceanic Iodine Emissions.

The influence of organic compounds on iodine (I2) emissions from the O3 + I– reaction at the sea surface was investigated in laboratory and modeling studies using artificial solutions, natural subsurface seawater (SSW), and, for the first time, samples of the surface microlayer (SML). Gas-phase I2 was measured directly above the surface of liquid samples using broadband cavity enhanced absorption spectroscopy. I2 emissions were consistently lower for artificial seawater (AS) than buffered potassium iodide (KI) solutions. Natural seawater samples showed the strongest reduction of I2 emissions compared to artificial solutions with equivalent [I–], and the reduction was more pronounced over SML than SSW. Emissions of volatile organic iodine (VOI) were highest from SML samples but remained a negligible fraction (<1%) of the total iodine flux. Therefore, reduced iodine emissions from natural seawater cannot be explained by chemical losses of I2 or hypoiodous acid (HOI), leading to VOI. An interfacial model explains this reduction by increased solubility of the I2 product in the organic-rich interfacial layer of seawater. Our results highlight the importance of using environmentally representative concentrations in studies of the O3 + I– reaction and demonstrate the influence the SML exerts on emissions of iodine and potentially other volatile species.

Large Enrichment of Anthropogenic Organic Matter Degrading Bacteria in the Sea-Surface Microlayer at Coastal Livingston Island (Antarctica).

The composition of bacteria inhabiting the sea-surface microlayer (SML) is poorly characterized globally and yet undescribed for the Southern Ocean, despite their relevance for the biogeochemistry of the surface ocean. We report the abundances and diversity of bacteria inhabiting the SML and the subsurface waters (SSL) determined from a unique sample set from a polar coastal ecosystem (Livingston Island, Antarctica). From early to late austral summer (January–March 2018), we consistently found a higher abundance of bacteria in the SML than in the SSL. The SML was enriched in some Gammaproteobacteria genus such as Pseudoalteromonas, Pseudomonas, and Colwellia, known to degrade a wide range of semivolatile, hydrophobic, and surfactant-like organic pollutants. Hydrocarbons and other synthetic chemicals including surfactants, such as perfluoroalkyl substances (PFAS), reach remote marine environments by atmospheric transport and deposition and by oceanic currents, and are known to accumulate in the SML. Relative abundances of specific SML-enriched bacterial groups were significantly correlated to concentrations of PFASs, taken as a proxy of hydrophobic anthropogenic pollutants present in the SML and its stability. Our observations provide evidence for an important pollutant-bacteria interaction in the marine SML. Given that pollutant emissions have increased during the Anthropocene, our results point to the need to assess chemical pollution as a factor modulating marine microbiomes in the contemporaneous and future oceans.

Sources and Sinks of Isoprene in the Global Open Ocean: Simulated Patterns and Emissions to the Atmosphere

AbstractThe ocean is a source of isoprene to the atmosphere. Although their global estimates are relatively low compared with the terrestrial source, these emissions have an influence on atmospheric chemistry. The lack of knowledge about the sources and sinks of isoprene in the ocean has hitherto precluded a precise assessment of when and where these emissions might be significant. Here we use the general circulation and biogeochemistry model Nucleus for European Modelling of the Ocean, Pelagic Interaction Scheme for Carbon and Ecosystem Studies (NEMO‐PISCES) to explore different parameterizations of the 3D oceanic sources and sinks of isoprene. In addition, we investigate a representation of the isoprene emission due to photoproduction in the sea surface microlayer. Our model estimates are complemented by a new data compilation of laboratory isoprene production rates and in situ isoprene concentrations. This study constitutes the first attempt to simulate isoprene in a global 3D ocean biogeochemical model. We find that sea surface temperature is an important driver modulating phytoplankton isoprene production and that light levels only play a secondary role at the scale of the global ocean. Furthermore, the use of a variable biochemical consumption rate improves the model‐data comparison. We show the importance of isoprene production below the mixed layer and, as a consequence, demonstrate that models based on 2D surface satellite chlorophyll‐a could miss up to 18.5% of oceanic isoprene emissions. The oceanic isoprene emissions to the atmosphere are estimated to 0.66 (0.43–0.82) Tg C yr−1 in the low range of previous estimates.

Enrichment of perfluoroalkyl substances in the sea-surface microlayer and sea-spray aerosols in the Southern Ocean

Sea-spray (or sea-salt) aerosol (SSA) formation and their subsequent atmospheric transport and deposition have been suggested to play a prominent role in the occurrence of ionizable perfluoroalkyl substances (PFAS) in the maritime Antarctica and other remote regions. However, field studies on SSA’s role as vector of transport of PFAS are lacking. Following a multiphase approach, seawater (SW), the sea-surface microlayer (SML) and SSA were sampled simultaneously at South Bay (Livingston Island, Antarctica). Average PFAS concentrations were 313 pg L−1, 447 pg L−1, and 0.67 pg m−3 in SW, the SML and SSA, respectively. The enrichment factors of PFAS in the SML and SSA ranged between 1.2 and 5, and between 522 and 4690, respectively. This amplification of concentrations in the SML is consistent with the surfactant properties of PFAS, while the large enrichment of PFAS in atmospheric SSA may be facilitated by the large surface area of SSA and the sorption of PFAS to aerosol organic matter. This is the first field work assessing the simultaneous occurrence of PFAS in SW, the SML and SSA. The large measured amplification of concentrations in marine aerosols supports the role of SSA as a relevant vector for long-range atmospheric transport of PFAS.

Identification of tidal trapping of microplastics in a temperate salt marsh system using sea surface microlayer sampling

Microplastics are contaminants of increasing global environmental concern. Estuaries are a major transport pathway for land-derived plastics to the open ocean but are relatively understudied compared to coastal and open marine environments. The role of the “estuarine filter”, by which the supply of sediments and contaminants to the sea is moderated by processes including vegetative trapping and particle flocculation, remains poorly defined for microplastics land to sea transfer. Here, we focus on the sea surface microlayer (SML) as a vector for microplastics, and use SML sampling to assess microplastic trapping in a temperate marsh system in Southampton Water, UK. The SML is known to concentrate microplastics relative to the underlying water and is the first part of rising tidal waters to traverse intertidal and upper tidal surfaces. Sampling a salt marsh creek at high temporal resolution allowed assessment of microplastics in-wash and outflow from the salt marsh, and its relationship with tidal state and bulk suspended sediment concentrations (SSC), over spring and neap tides. A statistically significant decrease in microplastics abundance from the flood tide to the ebb tide was found, and a weak positive relationship with SSC observed.

Sea surface phytoplankton community response to nutrient and light changes

The sea surface microlayer (SML) is the boundary layer between the ocean and the atmosphere and plays a unique role in marine biogeochemistry. Phytoplankton communities in this uppermost surface layer are exposed to extreme ultraviolet (UV) radiation and potentially high nutrient supplies. In order to understand the response of SML communities to such contrasting conditions, we conducted experiments at three different sites, the North Sea (open ocean) and two sites, outer and middle fjord, in the Sognefjord, Norway, with differing physical and chemical parameters. We manipulated light, nitrogen (N) and phosphorus (P) supply to natural communities collected from the SML and compared their response to that of the underlying water (ULW) communities at 1-m depth. Phytoplankton communities in both SML and ULW responded significantly to N addition, suggesting the upper 1-m surface phytoplankton communities were N-limited. While phytoplankton growth rates were higher with high N and high light supply, biomass yield was higher under low light conditions and with a combined N and P supply. Furthermore, biomass yield was generally higher in the ULW communities compared to SML communities. Nutrient and light effects on phytoplankton growth rates, particulate organic carbon (POC) and stoichiometry varied with geographical location. Phytoplankton growth rates in both SML and ULW at the open ocean station, the site with highest salinity, did not respond to light changes, whereas the communities in the middle fjord, characterized by high turbidity and low salinity, did experience light limitation. This work on the upper surface phytoplankton communities provides new insights into possible effects of coastal darkening and increases understanding of oceanic biogeochemical cycling.

Foamed Polystyrene in the Marine Environment: Sources, Additives, Transport, Behavior, and Impacts

Foamed polystyrene (PS) that may be either expanded (EPS) or extruded (XPS) is a rigid, lightweight insulating thermoplastic that has a variety of uses in the consumer, packaging, construction, and marine sectors. The properties of the material also result in waste that is readily generated, dispersed, and fragmented in the environment. This review focuses on foamed PS in the marine setting, including its sources, transport, degradation, acquisition of contaminants, ingestion by animals, and biological impacts arising from the mobilization of chemical additives. In the ocean, foamed PS is subject to wind-assisted transport and fracturing via photolytic degradation. The material may also act as a substrate for rafting organisms while being exposed to elevated concentrations of natural and anthropogenic surface-active chemicals in the sea surface microlayer. In the littoral setting, fragmentation is accentuated by milling in the swash zone and abrasion when beached, with wind transport leading to the temporary burial of significant quantities of material. Ingestion of EPS and XPS has been documented for a variety of marine animals, but principally those that feed at the sea surface or use the material as a habitat. As well as risking injuries due to gastro-intestinal blockage, ingestion of foamed PS exposes animals to harmful chemicals, and of greatest concern in this respect is the presence of the historical, but still recycled, flame-retardant, hexabromocyclododecane. Because foamed PS is particularly difficult to retrieve as a constituent of marine litter, means of reducing its presence and impacts will rely on the elimination of processes that generate foamed waste, modification of current storage and disposal practices, and the development of more durable and sustainable alternatives.

Sandaracinobacter neustonicus sp. nov., isolated from the sea surface microlayer in the Southwestern Pacific Ocean, and emended description of the genus Sandaracinobacter.

A Gram-stain-negative, non-motile, facultatively anaerobic and rod-shaped bacterial strain, designated PAMC 28131T, was isolated from a sea surface microlayer sample in the open water of the Pacific Ocean. Phylogenetic analysis of the 16S rRNA gene sequence of strain PAMC 28131T revealed an affiliation to the genus Sandaracinobacter with the closest species Sandaracinobacter sibiricus RB16-17T (sequence similarity of 98.2 %). Strain PAMC 28131T was able to grow optimally with 0.5-1.0 % NaCl and at pH 6.5-7.0 and 30 °C. The polar lipids were phosphatidylglycerol, phosphatidylethanolamine, two unidentified phospholipids, an unidentified aminolipid, an unidentified glycolipid and an unidentified lipid. The major cellular fatty acids (>10 %) were C18 : 1 ω6c and/or C18 : 1 ω7c, (42.6 %), C17 : 1 ω6c (19.3 %) and C16 : 1 ω6c and/or C16 : 1 ω7c (15.8 %), and the respiratory quinone was Q-10. The genomic DNA G+C content was 65.3 mol%. The phylogenetic, phenotypic and chemotaxonomic data showed that strain PAMC 28131T could be clearly distinguished from S. sibiricus RB16-17T. Thus, strain PAMC 28131T should be classified as representing a novel species in the genus Sandaracinobacter, for which the name Sandaracinobacter neustonicus sp. nov. is proposed. The type strain is PAMC 28131T (=KCCM 43127T=JCM 30734T).