Description: The transit of RV SONNE from Las Palmas (departure: 11.12.2021) to Guayaquil, Ecuador (arrival: 11.01.2022) is directly related to the international collaborative project SO287-CONNECT of GEOMAR in cooperation with Hereon and the University of Bremen, supported by the German Federal Ministry of Education and Research (BMBF) between October 15 2021 and January 15 2024. The research expedition was conducted to decipher the coupling of biogeochemical and ecological processes and their influence on atmospheric chemistry along the transport pathway of water from the upwelling zones off Africa into the Sargasso Sea and further to the Caribbean and the equatorial Pacific. Nutrient-rich water rises from the deep and promotes the growth of plant and animal microorganisms, and fish at the ocean surface off West Africa. The North Equatorial Current water carries the water from the upwelling, which contains large amounts of organic material across the Atlantic to the Caribbean, supporting bacterial activity along the way. But how the nutritious remnants of algae and other substances are processed on their long journey, biochemically transformed, decomposed into nutrients and respired to carbon dioxide, has so far only been partially investigated. Air, seawater and particles were sampled in order to provide new details about the large cycles of carbon and nitrogen, but also of many other elements such as oxygen, iodine, bromine and sulfur. Inorganic and organic bromine and iodine compounds are generally emitted naturally from the ocean into the atmosphere, promote cloud formation and affect climate, and some even reach the stratosphere where they contribute to ozone depletion. We measured how much of these compounds are released from the ocean, and at what locations and how they are transformed in the ocean and in the atmosphere. Sargassum algae, which have become a nuisance on beaches in the western and eastern Atlantic, support life and contribute to carbon cycling in the middle of the Atlantic, the Sargasso Sea and in the Caribbean, while their contribution to halogen cycling and marine bromine and iodine emissions was previously unknown. We investigated the influence of various natural parameters such as temperature and solar radiation on the biogeochemical transformation processes in order to understand the influence of climate change on these processes in incubation experiments with seawater and algae. We investigated how anthropogenic signals such as shipping traffic influence the nitrogen and sulphur cycle in the ocean, as well as the impact of nitrogen oxides from ship exhaust and sulphurous, acidic and dirty water from purification systems on organisms and biochemical processes. Plastic debris was sampled from the surface waters to investigate its contribution to global biogeochemical transformation processes. The working hypotheses of the research program were:  Bioavailability of dissolved organic carbon in surface waters decreases along the productivity gradient and transport pathway from the Eastern to the Western Tropical North Atlantic.  Nutrient gradients from East to West constrain the microbial utilization of organic matter- contributing to an accumulation of C-rich organic matter due to a) limited mineralization and b) enhanced exudation- also leading to gel-like particles accumulation in the western tropical North Atlantic and Sargasso Sea.  Tropospheric and stratospheric ozone are strongly impacted by biogeochemical and ecological processes occurring around and in the NA gyre system related to marine iodine and bromine cycles.  The long-range transport of natural and anthropogenic organic matter in water and of gases and aerosols in the air impact carbon-export, biogeochemical cycles in the water column, and the release of gases and particles from the ocean significantly. 4 SONNE -Berichte, SO287, Las Palmas - Guayaquil, 11.12.2021 - 11.01.202 The data and samples obtained specifically target carbon, nutrient and halogen cycling, the composition of phytoplankton, bacteria, the transport and sequestration of macro algae and the air-sea exchange processes of climate relevant gases and aerosols. The influence of ecological and transport processes, as well as anthropogenic impacts on the North Atlantic gyre system, specifically in the Sargasso Sea and the influence of ship emissions throughout the Atlantic towards the west and into the Pacific will be investigated with the data.

Description: 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.

Description: We use isoprene and related field measurements from three different ocean data sets together with remotely sensed satellite data to model global marine isoprene emissions. We show that using monthly mean satellite-derived chl a concentrations to parameterize isoprene with a constant chl a normalized isoprene production rate underpredicts the measured oceanic isoprene concentration by a mean factor of 19 ± 12. Improving the model by using phytoplankton functional type dependent production values and by decreasing the bacterial degradation rate of isoprene in the water column results in only a slight underestimation (factor 1.7 ± 1.2). We calculate global isoprene emissions of 0.21 Tg C for 2014 using this improved model, which is twice the value calculated using the original model. Nonetheless, the sea-to-air fluxes have to be at least 1 order of magnitude higher to account for measured atmospheric isoprene mixing ratios. These findings suggest that there is at least one missing oceanic source of isoprene and, possibly, other unknown factors in the ocean or atmosphere influencing the atmospheric values. The discrepancy between calculated fluxes and atmospheric observations must be reconciled in order to fully understand the importance of marine-derived isoprene as a precursor to remote marine boundary layer particle formation.

Description: The climate active trace-gas carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere. A missing source in its atmospheric budget is currently suggested, resulting from an upward revision of the vegetation sink. Tropical oceanic emissions have been proposed to close the resulting gap in the atmospheric budget. We present a bottom-up approach including (i) new observations of OCS in surface waters of the tropical Atlantic, Pacific and Indian oceans and (ii) a further improved global box model to show that direct OCS emissions are unlikely to account for the missing source. The box model suggests an undersaturation of the surface water with respect to OCS integrated over the entire tropical ocean area and, further, global annual direct emissions of OCS well below that suggested by top-down estimates. In addition, we discuss the potential of indirect emission from CS2 and dimethylsulfide (DMS) to account for the gap in the atmospheric budget. This bottom-up estimate of oceanic emissions has implications for using OCS as a proxy for global terrestrial CO2 uptake, which is currently impeded by the inadequate quantification of atmospheric OCS sources and sinks.

Description: Aufgrund der großen Variabilität des marinen DMS-Kreislaufs und den damit verbundenen Interaktionen zwischen Ozean und Atmosphäre sind noch viele Fragen, vor allem in Bezug auf die Saisonalität von DMS, DMSP und DMSO offen. In dieser Arbeit sollte die Saisonalität von Dimethylsulfid (DMS), dessen chemischen Ausgangsstoffs Dimethylsulfoniopropionat (DMSP) und dessen Oxidationsprodukts Dimethylsulfoxid (DMSO) an der Zeitserienstation Boknis Eck im Zeitraum Februar 2009 bis August 2010 untersucht werden. Die Konzentrationen von DMS an der Oberfläche reichten von 0,3 nmol L-1 im Winter (Januar 2010) bis 6,7 nmol L-1 im Sommer (August 2010). Die Konzentrationen von DMSP zeigten, wie auch die DMS-Konzentrationen, eine saisonale Schwankung mit hohen Konzentrationen(79,2 nmol L-1) im Herbst und geringeren Konzentrationen bei der Frühlingsblüte im März (19,6 nmol L-1), wohingegen im Winter die Konzentrationen bei etwa 5 nmol L-1 (Januar 2010) lagen. Die Ergebnisse passen mit den Saisonalitäten der Nährstoffe, wie Nitrat, Phosphat oder Silikat zusammen, die im Frühling und Herbst durch die Wasserdurchmischung an die Oberfläche gelangen und dort dem Phytoplankton als Nahrung zur Verfügung stehen. Die Konzentrationen von DMSO konnten nur jeweils von April bis Juli in beiden Jahren verglichen werden und zeigten beide ein Konzentrationsmaximum im Juni (ca. 25 nmol L-1 2009; ca. 50 nmol L-1 2010), wobei in den oberen 10 m die Konzentration im untersuchten Zeitraum 2010 in etwa doppelt so groß war, wie noch im Jahr 2009. Diese Unterschiede konnten auf hohe Konzentrationen von DMSP zurückgeführt werden. Es zeigte sich, dass die DMSP-Konzentrationen aufgrund des saisonalen Verlaufs mit der biologischen Aktivität zusammenhängen, jedoch konnte keine saisonal durchgängige Korrelation mit den Konzentrationen von Chlorophyll a weder für DMSP noch für DMS und DMSO gefunden werden. Grund dafür sind die verschiedenen Phytoplanktonarten, die jeweils unterschiedlich viel DMSP produzieren. So kann eine kleine Blüte mit DMSPproduzierenden Arten eine höhere Konzentration hervorrufen, als eine starke Phytoplanktonblüte mit Arten, die wenig, bzw. kein DMSP produzieren.