Succession of the sea-surface microlayer in the coastal Baltic Sea under natural and experimentally induced low-wind conditions

摘要

The sea-surface microlayer (SML) is located within the boundary between theatmosphere and hydrosphere. The high spatial and temporal variability of theSML's properties, however, have hindered a clear understanding ofinteractions between biotic and abiotic parameters at or across theair-water interface. Among the factors changing the physical and chemicalenvironment of the SML, wind speed is an important one. In order to examinethe temporal effects of minimized wind influence, SML samples were obtainedfrom the coastal zone of the southern Baltic Sea and from mesocosmexperiments in a marina to study naturally and artificially calmed seasurfaces. Organic matter concentrations as well as abundance,3H-thymidine incorporation, and the community composition of bacteriain the SML (bacterioneuston) compared to the underlying bulk water (ULW)were analyzed. In all SML samples, dissolved organic carbon and nitrogenwere only slightly enriched and showed low temporal variability, whereasparticulate organic carbon and nitrogen were generally greatly enriched andhighly variable. This was especially pronounced in a dense surface film(slick) that developed during calm weather conditions as well as in theartificially calmed mesocosms. Overall, bacterioneuston abundance andproductivity correlated with changing concentrations of particulate organicmatter. Moreover, changes in the community composition in the field studywere stronger in the particle-attached than in the non-attachedbacterioneuston. This implies that decreasing wind enhances the importanceof particle-attached assemblages and finally induces a succession of thebacterial community in the SML. Eventually, under very calm meteorologicalconditions, there is an uncoupling of the bacterioneuston from the ULW.