The cycling of carbon, oxygen, nitrogen and other macro-/micro-nutrients in the world's oceans and other aquatic systems is undergoing unprecedented change as a result of anthropogenic pressures. Observations and future projections of the complex interactions within these biogeochemical cycles and their perturbations at all spatiotemporal scales will help us to understand the implications of future changes for ocean, coastal and freshwater ecosystems and their sustainability. Such an improved understanding is essential to the development of model applications for monitoring their biogeochemical state, the management of living resources and ecosystems for research as well as operational applications. This session will bring together researchers that use a range of novel techniques, including observations (e.g. in-situ measurements, remote sensing, global syntheses), experiments (e.g. laboratory and mesocosms), and modeling approaches (e.g. Earth System models and ecosystem models) to further our understanding of the biological carbon-pump, the biogeochemical cycles, their connections to ecosystems and climate, as well as the potential for the development of operational applications. We welcome contributions (1) dealing with the cycling of carbon, oxygen, nitrogen, and other macro-/micro-nutrients in the ocean and other aquatic systems, dissolved and particulate stoichiometry and elemental ratios, primary production, ocean acidification, exchange processes at the air-sea interface, role of sea-ice in global biogeochemical cycles and synthesis studies including those using global data sets such as SOCAT and GLODAP; as well as (2) exploring innovative approaches to model-data fusion (e.g. novel methods in data assimilation, assimilation of data from novel in-situ or remote platforms, assimilation of up- or down-stream products of ocean color remote sensing), model skill assessment, downscaling from large to regional domains, and case studies of research and operational applications (e.g. HAB prediction, episodic hypoxia, management of marine and freshwater living resources).