Control of Earth’s climate(s) by the polar Southern Ocean

How much heat and carbon will be taken up by the ocean in the future? This is one of the most pressing questions the scientific community must answer in order to help human society to predict and adapt to global warming. On multidecadal to millennial time scales, the answer mostly lies in the polar (south of ~60S) Southern Ocean. Here, very dense water forms near the Antarctic coast and sinks to the abyss, driving the lower limb of the global overturning circulation and determining the ocean’s ability to sequester heat and carbon in the abyss for centuries. However, a robust quantitative understanding of the mechanisms underpinning abyssal ventilation in the pSO is lacking, mainly due to the formidable challenges to the collection of measurements in this harsh and remote environment. The project aims to 1) generate a state-of-the-art, baseline estimate of the rate of pSO overturning and abyssal heat sequestration, 2) quantify air-sea CO2 exchange and abyssal carbon ventilation in the Southern Ocean, and identify their key controlling processes, and 3) assess how melting of the Antarctic Ice Sheet influences heat and carbon sequestration in the abyssal Southern Ocean. Given the polar Southern Ocean regulates climate on long time scales, this new knowledge will be used to test mechanisms of glacial-interglacial transitions and abrupt past climatic changes. This project thus aims to better understand past climate transitions, opening the way for better predicting the long-term (> 50 years) future of the Earth’s climate system.