Contribution of surface wave-induced vertical mixing to heat content in global upper ocean

Abstract

Compared with observations, the simulated upper ocean heat content (OHC) determined from climate models shows an underestimation bias. The simulation bias of the average annual water temperature in the upper 300 m is 0.2°C lower than the observational results. The results from our two numerical experiments, using a CMIP5 model, show that the non-breaking surface wave-induced vertical mixing can reduce this bias. The enhanced vertical mixing increases the OHC in the global upper ocean (65°S–65°N). Using non-breaking surface wave-induced vertical mixing reduced the disparity by 30% to 0.14°C. The heat content increase is not directly induced by air-sea heat fluxes during the simulation period, but is the legacy of temperature increases in the first 150 years. During this period, additional vertical mixing was initially included in the climate model. The non-breaking surface wave-induced vertical mixing improves the OHC by increasing the air-sea heat fluxes in the first 150 years. This increase in air-sea heat fluxes warms the upper ocean by 0.05–0.06°C. The results show that the incorporation of vertical mixing induced by nonbreaking surface waves in our experiments can improve the simulation of OHC in the global upper ocean.