Comment on egusphere-2022-387

Abstract

The ocean responds to climate change through modifications of heat, freshwater and momentum fluxes at its boundaries. The role of these contributors in changing the thermohaline structure of the ocean and its circulation has been partly addressed by modeling studies using idealized CO2 forcings. The question of timescales for these individual contributions during transient climate change is however lacking. Here, we propose a novel modeling framework to isolate these contributions during the entire historical period and projections of coupled climate models. We present the framework in the context of the IPSL-CM6A-LR model and its ocean component NEMO3.6. We start by reproducing a coupled pre-industrial control simulation with an ocean-only configuration, forced by fixed fluxes at its interface diagnosed from the coupled model. We then add a perturbation to each flux component, extracted from the historical+ssp ensemble of simulations of IPSL-CM6A-LR. With this configuration, we successfully replicate the ocean's response to transient climate change in the coupled model during 1850–2100. This full response is then decomposed in sensitivity experiments in which the perturbations are applied individually to the heat, freshwater and momentum fluxes. Passive tracers of temperature and salinity are implemented to discriminate the addition of heat and freshwater flux anomalies in the ocean from the redistribution of pre-industrial heat and salt content in response to ocean circulation changes. This framework brings new opportunities to precisely explore the mechanisms driving transient ocean changes within single climate models.