Biochemical processes and Air-sea exchange in the SML (BASS)

The surface of the oceans is covered by an extremely thin layer of water through which the exchange of substances between air and water takes place. Extreme conditions prevail at this interface, with very rapid fluctuations in temperature and salinity over the course of the day. The microbes living here, above all the bacteria, are also exposed to extreme stress from cell- damaging ultraviolet radiation when the weather is nice. Bacteria perform an important task in the sea because they can bind dissolved organic carbon in the cell. However, most of the carbon taken up is converted to carbon dioxide and released into the water. Depending on the stress level of the bacteria, more or less dissolved organic carbon is bound and thus bacteria in the sea can increase or decrease the concentration of climate- damaging CO2. In addition, bacteria have the ability to change dissolved organic material in such a way that it can no longer be quickly utilized by other microbes and thus is stored in the water column for a long time. Previous research suggests that specific microbial communities live in the oceanic surface skin, some of which can withstand the harsh environmental conditions. However, we do not yet know which specific bacteria these are and whether there are genetic adaptations that allow them to survive environmental extremes relatively unscathed. This is where our project comes in and, in a first step, investigates which microbial communities are present in the boundary layer and how far they differ from the underlying water. Then we measure the activity, growth rates and respiration of the bacteria under different weather conditions to find out what influence climate fluctuations have on the bacteria. Subsequently, we try to cultivate bacteria that we were able to identify from the genetic analysis as being characteristic of the surface skin. Laboratory experiments with a defined UV radiation and subsequent physiological investigations show us adaptations or protective mechanisms of the bacteria. We use the latest molecular tools that allow us to decode the function of genes and proteins in the bacterial community. Another innovation in the project is a self-propelled catamaran that can collect many liters of the thin surface layer in a very short time. Our ultimate goal is to understand the cycling of organic matter in the interface between the atmosphere and seawater in order to better predict future climate. Our planned investigations will underscore the important role played by the bacterial community in the surface skin of the oceans.