The global ocean is the largest energy reservoir in the Earth system, and is responsible for more than 9/10ths of Earth’s observed heat uptake. While the bulk of this additional heat accumulation over the longer term (1960s-present) is now found in the ocean, and this result can be replicated across multiple observations and models, an evaluation of where this heat resides through the vertical distribution and throughout the ocean basins is not well known.

In this study we consider the upper (0-700m), intermediate (700-2000m) and deep (2000m - bottom), and investigate temperature changes through the global ocean in available observations and the historical simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5). While models do capture changes through the full-depth profile, deep changes are often confounded by climate drift, which needs to be considered before change estimates can be ascertained.

This presentation will expand on earlier results which considered global averaged changes through ocean depth, and consider the large, basin-scale changes from the upper ocean through to the abyss. The analysis is timely as Argo, the fleet of autonomous profiling floats that observes temperature and salinity in the global ocean from the surface to 2 km depth is currently expanding into the deeper ocean. This Argo network has greatly improved the ability to quantify upper and intermediate ocean warming since it first achieved sparse global coverage in 2005. However, deep ocean warming, which is also simulated by climate models, and has been observed in recent decades by repeat hydrographic sections is now being addressed by Deep Argo (sampling to the ocean floor). If Deep Argo is implemented globally it should markedly increase the temporal frequency of deep ocean observational coverage and reduce uncertainties in ocean observations below the present 2 km depth limit of Argo.