Trace metals function as essential micronutrients and pollutants in the ocean. Organic complexation, size partitioning, and redox changes of trace elements can be mediated by biological processes including uptake, regeneration, cell lysis, and organic ligand production. Additional processes influencing the production, degradation, and composition of organic matter also play an important role in controlling trace metal distributions, and both vary across environments (e.g. estuaries, open ocean, air-sea-sediment interfaces, hydrothermal systems). In turn, resulting changes in bioavailability and cycling of trace elements governs the function and composition of marine phytoplankton communities. Recent efforts, particularly within GEOTRACES, have expanded the database of trace metal concentrations and physicochemical speciation. This session seeks to link our understanding of biology, organic matter, and trace metal chemistry from molecular to basin-wide scales, from studies related to biologically-mediated transformations of trace elements to the wider processes controlling metal distributions, size partitioning, and fluxes. We welcome submissions highlighting how marine organisms influence the physicochemical speciation of trace elements in seawater, and how changes in trace element chemistry impact the structure and function of marine ecosystems. In addition to observational, experimental and modelling studies, we also invite contributions on the production, degradation, and characterization of metal-binding compounds and colloids.