The cycling of carbon, oxygen, and nitrogen in the world's oceans 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 spatio-temporal scales will help us to understand the implications of future changes for marine ecosystems and ocean sustainability. Such an improved understanding is essential to the development of model applications for monitoring the ocean biogeochemical state, the management of marine living resources and ocean 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 technologies, remote platforms, global data sets), experiments, and modeling approaches to further our understanding of the biological carbon-pump, the biogeochemical cycles in the ocean, 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, and nitrogen in the ocean, dissolved and particulate stoichiometry and elemental ratios, 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 downstream 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, ocean acidification, management of marine living resources).