Via their fundamental control on ocean productivity and the biological carbon pump, the cycling of nutrients plays an integral role in the dynamics of atmospheric CO2 and climate. In contrast to the ‘big three’- nitrogen, phosphorus and silicon, with their well characterised modern distributions and relatively stable inventories, micronutrients, such as iron, remain relatively poorly observed and have the potential for rapid and profound changes in their inventories and biological availability in response to a host of poorly constrained processes. Micronutrients are currently the ‘wild card’ in both past and future carbon cycle and climate change, prompting the need for improved understanding of their role in Earth system dynamics. We invite a broad range of submissions to provide insights into the pieces of the puzzle, addressing boundary inputs and sinks, exchanges between dissolved and solid phases, interactions with organic compounds, and their reciprocal interactions with microbial ecosystems. Submissions may include observations, data synthesis or models, and may address ocean nutrient cycling over a range of time-scales, from past (paleo) through contemporary, and/or in response to future global change. We particularly encourage new insights into the role of feedbacks and the role micronutrient cycles play in shaping global-scale dynamics.