UC San Diego

This thesis explores the physical connections between surface processes and the global ocean overturning circulation, which is a critical component of the climate system.

Chapter 2 discusses the influence of Southern Ocean surface buoyancy forcing on the global deep ocean stratification. It shows that Southern Ocean surface buoyancy forcing exerts a strong control on the global deep ocean stratification below 2000 m depth.

Chapter 3 investigates the impact of Southern Ocean surface buoyancy forcing on the depth of the Atlantic Meridional Overturning Circulation (AMOC). It concludes that diapycnal mixing diminishes the influence of Southern Ocean surface buoyancy forcing on the AMOC depth and that the North Atlantic surface conditions can have a substantial influence on the AMOC depth.

Chapter 4 explores the influence of North Atlantic surface conditions on the Southern Ocean circulation. It highlights the importance of North Atlantic surface conditions in shaping the AMOC vertical structure.

Chapter 5 develops a framework that connects the AMOC depth to the surface density distributions in both the Southern Ocean and the North Atlantic.

Chapter 6 examines the role of the Southern Ocean in the AMOC variability. It highlights the importance of the Indo-Pacific ocean when the overturning circulation is not in steady state. Using a variety of models, it shows that changes in the Indo-Pacific component of the overturning circulation can compensate changes in the AMOC. This compensation decreases as the variability timescale becomes longer.

Chapter 7 is on a somewhat different subject. It investigates the influence of sea ice velocity biases on the simulated Antarctic sea ice extent trend during recent decades. It uses a state-of-the-art coupled climate model with the simulated ice velocity field replaced with a satellite-derived observational estimate to show that correcting the ice velocity bias could substantially improve the simulated Antarctic sea ice extent changes.