Marine Selenium Cycling

Selenium (Se) is an essential trace element for humans. It has been estimated that emissions of gaseous forms of Se from marine microorganisms accounts for a large part of Se that is cycled in the atmosphere. The atmosphere is an important source of Se to the Earth’s surface via rainfall and can thereby supply agricultural systems and other ecosystems with this essential element. However, the mechanisms behind the production of volatile selenium by marine biota is not yet well understood. For example, there is currently very little quantitative and qualitative information available about the nature of the forms of volatile Se emitted, sea-to-air fluxes of Se, the specific role of marine microorganisms (i.e. marine algae and bacteria) in producing volatile and organic Se species, and how these processes are affected by environmental conditions. Furthermore, cycling of Se in seawater remains largely unknown due to a lack in measurements of chemical forms, especially organic forms, of Se in seawaters and within marine microorganisms (phytoplankton/bacteria assemblages).

This project studying marine Se cycling currently tackles these research gaps in various subprojects: (1) Chemical forms of Se (speciation) and biotransformation of Se in synthetic and natural seawaters as a function of different environmental factors. (2) Atmospheric fluxes of volatile organic Se species and mechanisms of Se biomethylation. (3) The role of marine microorganisms in producing volatile organic Se species, including elucidating intracellular Se speciation and the role of Se in the marine microalgae metabolism.

Each of these subprojects includes the development of new analytical methods to characterize Se speciation in environmental compartments, i.e. biota, seawater and atmosphere. These new methods are then implemented during several research cruises (Baltic Sea, Mediterranean Sea, Polar Waters) as well as laboratory experiments. The project will present an important advancement of our understanding of biogeochemical Se cycling in seawaters, and will especially give new insights on how Se is transformed chemically and biologically in seawater and emitted into the atmosphere. Furthermore, the data produced in this project will be crucial for the development of biogeochemical models that predict the transfer of selenium between different environmental compartments, i.e., biosphere, hydrosphere, and atmosphere.