Air-Sea Interactions

The air-sea interface defines more than 70% of the Earth's surface area. We still lack knowledge of the physical and biogeochemical interactions and feedbacks along this vast interface, which can mitigate and alter the consequences of anthropogenic greenhouse gas emission and climate warming. These knowledge gaps were identified in the IPCC 2013 and implemented in the global action plan of the Surface Ocean-Lower Atmosphere Study (SOLAS) community (SOLAS 2015-2025: Science Plan and Organization, Brévière, 2015) in which e.g. controls on air-sea gas exchange of greenhouse gases and the identification of feedback loops between the ocean and atmosphere are addressed as pressing issues. This incorporates understanding of 1) the sources and dynamics of surface-active substances (SA), which hamper gas exchange and 2) the production and emission of primary and secondary biogenic aerosols leading to cloud formation and thus provoking changes in the Earth's radiation budget. What makes these questions exceptionally challenging is their inherent interdisciplinarity and complexity. Large-scale phenomena like cloud formation and climate forcing may origin in local and transient (small-scale) biogeochemical dynamics. Furthermore, these questions require studies in contrasting regions, from pristine oceanic regions in the Southern hemisphere to investigate cloud formation to coastal regions, in which deep-water upwelling and shallow seas define the direction and magnitude of greenhouse gas fluxes. In cooperation with several international partners, who also complement atmospheric chemical and physical measurements, we aim to better understand these biogeochemical interactions by focusing on the upper surface ocean layer.

1) As part of the DFG Forschungsgruppe BASS (2022-2026), our PhD student Josefine Karnatz deciphers how different phytoplankton communities in the Baltic Sea and the North Sea affect the organic matter and SA concentration and composition in the uppermost ocean surface layer, the so called 'sea surface microlayer' (SML). Data from several research campaigns, e.g. a mesocosm study in the SURF facility of ICBM in Wilhelmshaven or the CenBASE cruise will be synthesized.

2) In 2023, Dr. Theresa Barthelmeß participated in an Antarctic research cruise (POLAR CHANGE), which was initiated by the Institute de Ciències del Mar, Barcelona. This project focuses on resolving the influence of phytoplankton communities on primary and secondary aerosol formation in the marginal sea ice zone of the Weddell Sea.

In the past project SEA2CLOUD (2020), Dr. Theresa Barthelmeß studied short-term surface ocean organic matter dynamics in the Southwest Pacific Ocean. Accompanying data suggested an overlooked significant source in the surface ocean triggering secondary aerosol formation based on nitrogen-containing precursors (Chamba et al., 2023). With the help of the Flexible GEOMAR Funds, we will continue our work on secondary aerosol formation and its biogenic source mechanisms in cooperation with Dr. Karine Sellegri, her team (Université Clermont Auvergne, CNRS, Laboratoire de Météorologie Physique), and collogues from GEOMAR (FB2/CH and FB1/PO).