1. Wochenbericht AL510

Forschungsreise „Baltic GasEx“ FS Alkor AL510 03.06.2018 – 16.06.2018: Wochenbericht für den Fahrtabschnitt 03.06.18 – 09.06.1

The influence of air-sea fluxes on atmospheric aerosols during the summer monsoon over the tropical Indian Ocean

During the summer monsoon, the western tropical Indian Ocean is predicted to be a hot spot for dimethylsulfide emissions, the major marine sulfur source to the atmosphere, and an important aerosol precursor. Other aerosol relevant fluxes, such as isoprene and sea spray, should also be enhanced, due to the steady strong winds during the monsoon. Marine air masses dominate the area during the summer monsoon, excluding the influence of continentally derived pollutants. During the SO234-2/235 cruise in the western tropical Indian Ocean from July to August 2014, directly measured eddy covariance DMS fluxes confirm that the area is a large source of sulfur to the atmosphere (cruise average 9.1 μmol m−2 d−1). The directly measured fluxes, as well as computed isoprene and sea spray fluxes, were combined with FLEXPART backward and forward trajectories to track the emissions in space and time. The fluxes show a significant positive correlation with aerosol data from the Terra and Suomi-NPP satellites, indicating a local influence of marine emissions on atmospheric aerosol numbers

Marines Isopren: Bildung, Emissionen und ihr Einfluss auf die Chemie in der Atmosphäre

Volatile organic compounds (VOCs) play an important role in influencing the oxidative capacity of the atmosphere. Isoprene, the most important biogenic VOC, has received increased attention in recent years as biogenic emissions of isoprene are the main contributor for secondary organic aerosols (SOA) formation. SOA in the atmosphere influence the radiative balance through scattering or absorption of solar radiation and, therefore, have a direct impact on the climate of our Earth’s system. The knowledge about the spatial and seasonal distribution of isoprene, as well as its production and consumption processes in the surface ocean, is still lacking and is crucial to quantify marine isoprene emissions. The main goal of this work was to increase the global dataset of marine isoprene measurements and provide a better understanding of the biogeochemical cycling in the surface ocean. This improved understanding was used to calculate the global surface isoprene distribution and the isoprene emission to the atmosphere in order to estimate the influence of marine isoprene on the Earth’s atmosphere and climate.Flüchtige organische Verbindungen (VOCs: volatile organic compounds) haben einen großen Einfluss auf die oxidative Kapazität der Atmosphäre. Isopren, als wichtigster Vertreter der biogenen VOCs, wurde in den letzten Jahren zunehmende Aufmerksamkeit zuteil, da es als wichtiger Vorläuferstoff für die Bildung von sekundären organischen Aerosolen (SOA: seconary organic aerosols) verantwortlich ist. In der Atmosphäre beeinflusst SOA durch Streuung und Absorption von Sonnenstrahlung die Strahlungsbilanz der Erde und hat somit einen direkten Einfluss auf das Klima. Ziel dieser Arbeit war es Messungen von Isopren im Ozean durchzuführen und die Prozesse sowohl zur Bildung als auch zum Abbau von Isopren im Oberflächenozean zu untersuchen. Die hieraus gewonnenen Erkenntnisse wurden genutzt, um sowohl die globale Konzentrationsverteilung von Isopren im Oberflächenozean als auch die resultierenden Emissionen in die Atmosphäre zu berechnen, und um somit schlussendlich den globalen Einfluss von ozeanischem Isopren auf das Klima der Erde abschätzen zu können

1.Wochenbericht AL516

Forschungsreise „Baltic GasEx“ FS Alkor AL516 12.09.2018 – 23.09.2018 Wochenbericht für den Fahrtabschnitt 12.09.18 – 16.09.1

Marine isoprene - Formation, emissions and their impact on the atmospheric chemistry

Volatile organic compounds (VOCs) play an important role in influencing the oxidative capacity of the atmosphere. Isoprene, the most important biogenic VOC, has received increased attention in recent years as biogenic emissions of isoprene are the main contributor for secondary organic aerosols (SOA) formation. SOA in the atmosphere influence the radiative balance through scattering or absorption of solar radiation and, therefore, have a direct impact on the climate of our Earth’s system. The knowledge about the spatial and seasonal distribution of isoprene, as well as its production and consumption processes in the surface ocean, is still lacking and is crucial to quantify marine isoprene emissions. The main goal of this work was to increase the global dataset of marine isoprene measurements and provide a better understanding of the biogeochemical cycling in the surface ocean. This improved understanding was used to calculate the global surface isoprene distribution and the isoprene emission to the atmosphere in order to estimate the influence of marine isoprene on the Earth’s atmosphere and climate

Identification and characterisation of isoprene-degrading bacteria in an estuarine environment

Approximately one-third of volatile organic compounds (VOCs) emitted to the atmosphere consists of isoprene, originating from the terrestrial and marine biosphere, with a profound effect on atmospheric chemistry. However, isoprene provides an abundant and largely unexplored source of carbon and energy for microbes. The potential for isoprene degradation in marine and estuarine samples from the Colne Estuary, UK, was investigated using DNA-Stable Isotope Probing (DNA-SIP). Analysis at two timepoints showed the development of communities dominated by Actinobacteria including members of the genera Mycobacterium, Rhodococcus, Microbacterium and Gordonia. Representative isolates, capable of growth on isoprene as sole carbon and energy source, were obtained from marine and estuarine locations, and isoprene-degrading strains of Gordonia and Mycobacterium were characterised physiologically and their genomes were sequenced. Genes predicted to be required for isoprene metabolism, including four-component isoprene monooxygenases (IsoMO), were identified and compared with previously characterised examples. Transcriptional and activity assays of strains growing on isoprene or alternative carbon sources showed that growth on isoprene is an inducible trait requiring a specific IsoMO. This study is the first to identify active isoprene degraders in estuarine and marine environments using DNA-SIP and to characterise marine isoprene-degrading bacteria at the physiological and molecular level

Seasonal study of the Small-Scale Variability of Dissolved Methane in the western Kiel Bight (Baltic Sea) during the European Heat Wave in 2018

Methane (CH4) is a climate-relevant atmospheric trace gas which is emitted to the atmosphere from coastal areas such as the Baltic Sea. The oceanic CH4 emission estimates are still associated with a high degree of uncertainty partly because the temporal and spatial variability of the CH4 distribution in the ocean surface layer is usually not known. In order to determine the small-scale variability of dissolved CH4 we set up a purge-and-trap system with a significantly improved precision for the CH4 concentration measurements. We measured the distribution of dissolved CH4 in the water column of the western Kiel Bight and Eckernförde Bay in June and September 2018. The top 1 m was sampled in high-resolution to determine potential small-scale CH4 concentration gradients within the mixed layer. CH4 concentrations throughout the water column of the western Kiel Bight and Eckernförde Bay were generally higher in September than in June. The increase of the CH4 concentrations in the bottom water was accompanied by a strong decrease in O2 concentrations which led to anoxic conditions favorable for microbial CH4 production in September. In summer 2018, northwestern Europe experienced a pronounced heatwave. However, we found no relationship between the anomalies of water temperature and excess CH4 in both the surface and the bottom layer at the site of the Boknis Eck Time-Series Station (Eckernförde Bay). Therefore, the 2018 European heatwave most likely did not affect the observed increase of the CH4 concentrations in the western Kiel Bight from June to September 2018. The high-resolution measurements of the CH4 concentrations in the upper 1 m of the water column were highly variable and showed no uniform decreasing or increasing gradients with water depth. Overall, our results show that the CH4 distribution in the water column of the western Kiel Bight and Eckernförde Bay is strongly affected by both large-scale temporal (i.e. seasonal) and small-scale spatial variabilities which need to be considered when quantifying the exchange of CH4 across the ocean/atmosphere interface

Identification and characterisation of isoprene-degrading bacteria in an estuarine environment

Approximately one-third of volatile organic compounds (VOCs) emitted to the atmosphere consists of isoprene, originating from the terrestrial and marine biosphere, with a profound effect on atmospheric chemistry. However, isoprene provides an abundant and largely unexplored source of carbon and energy for microbes. The potential for isoprene degradation in marine and estuarine samples from the Colne Estuary, UK, was investigated using DNA-Stable Isotope Probing (DNA-SIP). Analysis at two timepoints showed the development of communities dominated by Actinobacteria including members of the genera Mycobacterium, Rhodococcus, Microbacterium and Gordonia. Representative isolates, capable of growth on isoprene as sole carbon and energy source, were obtained from marine and estuarine locations, and isoprene-degrading strains of Gordonia and Mycobacterium were characterised physiologically and their genomes were sequenced. Genes predicted to be required for isoprene metabolism, including four-component isoprene monooxygenases (IsoMO), were identified and compared with previously characterised examples. Transcriptional and activity assays of strains growing on isoprene or alternative carbon sources showed that growth on isoprene is an inducible trait requiring a specific IsoMO. This study is the first to identify active isoprene degraders in estuarine and marine environments using DNA-SIP and to characterise marine isoprene-degrading bacteria at the physiological and molecular level