The ocean is a major sink of anthropogenic carbon and heat, and dissolved oxygen has declined across all ocean basins, with consequences for marine ecosystems and biogeochemical cycling. Oxygen, carbon, and heat are coupled through shared pathways of ventilation, circulation, and biological processes. Their regional-scale relationships, however, remain poorly constrained, because internal variability and redistribution can reinforce, mask, or decouple changes at regional scales. A multi-tracer perspective is therefore key to interpreting ongoing changes and projecting future changes in regional biogeochemistry and marine ecosystems. Here we propose a session that brings together the physical oceanography, biogeochemistry, and climate communities to examine how ocean physics and climate variability shape the coupled cycling of oxygen, carbon, and heat across paleo, present-day, and future climates, drawing on theory, observations, modeling, and data-driven approaches.

We seek contributions that investigate variability, trends, and coupling among oxygen, carbon, and heat from regional to global scales. Topics can include ocean carbon uptake and storage, ocean heat uptake and redistribution, deoxygenation, and the ecological and biogeochemical consequences of these changes. Contributions using historical reconstructions and uncertainty assessments, models, model–observation synthesis, proxy records, technological developments, oceanic and atmospheric integral constraints, and data-driven approaches are particularly encouraged, as are approaches that foster cross-cutting exchanges across the physical–biogeochemical disciplines. We also welcome contributions to deepen our mechanistic understanding in driving the changes, including the roles of ventilation, circulation, mixing, air–sea exchange, and biological processes; the use of oxygen, carbon, heat, and related tracers to diagnose these processes; and the influence of climate variability, such as ENSO and Pacific decadal variability, on their regional co-variability. This session connects to ongoing international efforts, including the CLIVAR-O2CH Research Focus and the Gridded Observational Dataset Intercomparison Project (GODIP), and aims to provide a forum for advancing an integrated understanding of physical–biogeochemical coupling in a changing ocean.