Pan-Atlantic connectivity of marine biogeochemical and ecological processes and the impact of anthropogenic pressures, SO287, 11.12.2021 - 11.01.2022, Las Palmas (Spain) - Guayaquil (Ecuador)

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

Iodine volatilisation from the ocean

Reactive iodine species (RIS) in the troposphere affect partitioning in the HOx and NOx chemical families and thereby alter the troposphere’s oxidising capacity. Recent research indicates the main source of RIS globally is the heterogeneous reaction between atmospheric ozone and aqueous iodide at the surface of the oceans. However, uncertainties remain because experimental studies reported in the literature generally use reagent concentrations substantially above ambient conditions. This project used a broadband cavity enhanced absorption spectroscopy (BBCEAS) instrument with the necessary sensitivity to directly detect molecular iodine produced from ambient concentrations of ozone reacting with iodide at concentrations similar to those in seawater. Laboratory work on synthetic seawater solutions confirmed previous results that iodine emissions (i) increase with increasing concentrations of iodide and ozone, and decreasing pH Another BBCEAS instrument made ambient air measurements over the open ocean aboard the RV Sonne during the research vessel’s SO287 transect across the Atlantic Ocean (Dec 2021–Jan 2022). The instrument achieved an impressive iodine detection limit of 0.9 ppt (parts per trillion, 1, 10-minute averaging). However, even in the absence of photolytic iodine losses, night-time I2 concentrations failed to be observed above this detection limit. BBCEAS timeseries of NO2, which absorbs at the same wavelengths as I2, showed low concentration over the open ocean ( Hypoiodous acid (HOI) is the other main RIS product of the ozone + iodide reaction. Attempts to generate HOI and detect HOI by BBCEAS at near-ultraviolet wavelengths were unsuccessful.</p