Although Re accumulation in anoxic environments has been known for decades and Re is used to reconstruct redox conditions in the Earth's atmosphere and oceans in the past, it is surprising that little or almost no work has been devoted to understanding Re biogeochemistry in oxic environments (with respect to the water column). The sediment signatures provide us with evidence of evanescent Re particles that form in the oxic water column but whose origin is unknown, although there is indication that they are formed by biological activity. Understanding the mechanism of their formation and preservation in the sediment would have significant implications for our understanding of the operating principle of the Re paleoredox proxy, where sedimentary Re signatures could be used not only as a paleoredox but also as a paleoproductivity indicator. We hypothesize that algae play an important role in the biogeochemical cycle of Re. The project will address the bioaccumulation potential of brown algae on the eastern Adriatic coast, focusing on investigating the similarities/differences between Re, iodine and the nitrogen cycle, as the biological role of Re (if any) is not yet known. The potential role of phytoplankton (diatoms due to their known phylogenetic link to brown algae) in the marine Re budget will also be investigated. Determining the mechanism of Re accumulation/uptake by marine macrophytes and phytoplankton is an important part of the project, where different analytical approaches (mass spectrometry, column chromatography, electrochemistry, X-ray absorption fine structure) will be used to elucidate the interactions of Re with the extra- or possibly intracellular matrix. The adsorption properties of clay minerals in relation to Re are also neglected, but the project will re-examine the role of clay minerals in relation to Re in marine sediments inventory.