Transient tracer-based Investigation of Circulation and Thermal Ocean Change (TICTOC)

The aim of TICTOC is to quantify recent changes in the uptake and redistribution of heat by the ocean using observations and models and the transient tracer-based approach, enabling improved projections of future climate and its regional impacts. The new approach will separate warming into an added temperature change (the direct response to increasing radiative forcing) and a redistributed change (largely due to circulation changes). The decomposition is analogous to the separation of oceanic carbon content into ‘anthropogenic’ and ‘natural’ changes.

We will use a framework that has been developed in the climate modelling community, treating heat as a passive tracer. We will make a novel application of this framework to observations using the passive nature of transient tracers (CFCs and SF6) and carbon isotopes. The size, strength and evolution of the passive tracer (determined by our analysis of observations and forced ocean models) will be used to improve model projections of sea level change.

TICTOC will deliver observational constraints on the distinct processes by which heat is redistributed by the ocean, allowing for both quantification of recent warming and understanding of its drivers. New ship-based observations of transient tracers will be conducted in the Atlantic Ocean. Using the new and existing observations, thermodynamic and inverse theory, and current activities in CMIP6, we will provide a global view of the added and redistributed temperature change. We will analyse regional temperature and consequent thermosteric sea level changes and use our observational description of the recent past to constrain projections of future regional sea level change.