| Summary: | The global ocean plays a crucial role in modulating Earth’s present and future climate. In addition, most anthropogenic heat is stored in the ocean, causing thermal expansion of seawater, and consequently raising the global mean sea level. However, there is a large disagreement across climate models in the projection of ocean heat content (OHC) change and sea level rise. Here, we investigate climate model spread in OHC change in response to surface flux perturbations applied to climate models as part of the Flux-Anomaly-Forced Model Intercomparison Project (FAFMIP) simulations. The inter-model spread in OHC change, decomposed by physical processes, is large where the OHC change (i.e., signal) is large in response to individual surface flux forcing anomalies and mostly at similar locations as in the control simulations. OHC spread per basin is largest in the Atlantic Ocean response to perturbed surface heat flux, and Southern Ocean has largest spread in response to perturbed surface freshwater and momentum fluxes. This study shows that the largest inter-model spread in the vertical transport of heat is from resolved and mesoscale advective processes, and it is mostly seen in the eddy energetic and frontal regions both with and without perturbed forcings. The regional spread in OHC change and resolved advection is ~2 times larger than the internal variability in response to surface heat flux perturbation and within the range of unforced (~internal) variability response to surface freshwater and wind stress forcing at most places.
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