Thermobaric instability: The role of the ocean in the last deglaciation

Abstract:

The last deglaciation was a two-step process, a sudden warming (Bolling-Allerod) followed by a gradual cooling over a 3000 year period (Younger Dryas), followed by another sudden warming to near-modern conditions. The ice sheets have been implicated in this rapid climate change, but a recent study of ancient corals has implicated the deep oceans (Thiagarajan et al. Abrupt pre-Bolling-Allerod warming and circulation changes in the deep ocean. Nature 511, 75-81, 2014). We will first review the climate data and then report on our numerical model, which seems to support the oceanic hypothesis. The mechanism is thermobaric instability, which depends on the increase of the thermal coefficient of expansion with depth and can lead to a sudden release of stored potential energy (Su and Ingersoll. Ocean Convective Available Potential Energy. Part I: Concept and Calculation, and Part II: Energetics of Thermobaric Convection. J. Phys. Oceanogr., submitted, 2014). The model is two-dimensional—a slice through a vertical plane. It has salt diffusion, temperature diffusion and viscous dissipation, and it conserves energy exactly—to the round off error of the machine. We have run our model with realistic parameters and will compare the results with the deglaciation record.