Ocean Modeling Perspectives of Multi-Decadal Ocean Deoxygenation and Heat Content Evolutions

Observational studies reveal substantial ocean deoxygenation and increase in heat content in the past decades. These two properties are known to be tightly connected under the historical period without accelerated warming. The Earth System Models (ESMs) struggle to simulate the observed trend in oxygen inventory (O₂-Inv) and the tight global O₂-heat relationship. One possible reason is the role of decadal climate variability. Climate variability could modulate upper ocean O₂-Inv and heat content on decadal timescales but the observed climate variability is not necessarily in phase in the ESM’s historical simulations due to the fact that the models have their own internal climate variability. Here we address the question how the decadal climate variability modulated upper ocean O₂-Inv and heat content from a suite of OMIP (Ocean Model Intercomparison Project) simulations. The two main focus of this study are 1) to analyze the decadal changes in global and regional upper ocean O₂-Inv and heat content based on the results from omip1 and couple of spun-up simulations along with the observations, and 2) evaluate the model’s equilibrium states diagnosing the full five cycles of the omip1 simulations. The model differences result in a range of physical and biogeochemical mean states, which lead to different decadal variation of O₂-Inv and heat content. The preliminary results indicate that the regional upper ocean O₂-heat relationship including mid to high-latitude regions such as the North Atlantic and the North Pacific oceans show opposite relationships between the models and observations. This may point to common biases in the processes represented in the models. We further diagnose what causes these opposite relationships based on the analysis of additional physical and biogeochemical tracers from the models. The results will provide guidance on accuracy and uncertainty of future deoxygenation and heat uptake projected in the ESMs.