Climate change is one of the most urgent issues facing humanity and life on Earth.

Whilst our everyday understanding of climate concerns the warmth of the atmosphere, the ocean is critical in controlling how our planet’s climate changes. This is because the ocean absorbs vast quantities of heat and carbon dioxide which, if they had remained in the atmosphere, would have greatly accelerated the rate of climatic change there.

Since the industrial revolution, the global ocean has absorbed around 30% of anthropogenic (human-produced) CO₂ emissions. In addition, 93% of the total extra heat in the Earth System since the onset of global warming has been absorbed by the ocean. This is equivalent to around 170 terawatts, the power that would be required for each of the 7 billion people on Earth to continuously operate sixteen 1500 watt hairdryers.

Improving climate prediction thus requires us to learn more about how the ocean works, and how it interacts with the atmosphere to control the split of heat and carbon between them. A key region in this context is the Southern Ocean, the vast sea that encircles Antarctica.

Although the Southern Ocean occupies only around 20% of the total ocean area, it absorbs about three-quarters of the heat that is taken into the ocean, and approximately half of the CO_2. This is because of its unique pattern of ocean circulation: it is the key region globally where deep waters upwell to the surface from 1-2 km down, allowing new water masses to form and sink back into the ocean interior. This exposure of old waters to the atmosphere, and the production of new waters, is fundamental to the exchanges of heat and carbon with the atmosphere. More information on how the Southern Ocean influences global climate can be found in a recent article in Nature; click here.

Graphic of the overturning circulation in the Southern Ocean, and the lateral flows around the Antarctic continent. (From Meredith, Geophysical Research Letters, 2016)

Despite this knowledge of the key role the Southern Ocean plays in global climate, there are many important unknowns. These include an incomplete understanding of the detailed mechanisms by which heat and carbon and transferred across the sea surface and drawn down into the interior, a lack of knowledge of the rates of these transfers and how they will change in future, and insufficient information of the distribution of the heat and carbon around the globe within the planetary-scale ocean circulation.

To address these issues, an £8.4M programme was funded by NERC: ‘Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports (ORCHESTRA)’. The project was led by the British Antarctic Survey, in partnership with National Oceanography Centre, British Geological Survey, Plymouth Marine Laboratory, the Centre for Polar Observation and Modelling (CPOM), the Sea Mammal Research Unit at the University of St Andrews and the UK Met Office, along with numerous national and international partners.

ORCHESTRA will spanned five years and used a combination of data collection, analyses, and computer simulations to radically improve our ability to measure, understand and predict the circulation of the Southern Ocean and its role in the global climate. It made unique and important new measurements in the Southern Ocean using a range of techniques, including use of RRS James Clark Ross, and deployments of autonomous surface and underwater vehicles, the BAS meteorological aircraft, and other innovative techniques for collecting data. It also involved the development and use of advanced ocean and climate simulations, to improve our ability to predict climatic change in coming decades.

This work was supported by the Natural Environment Research Council [ORCHESTRA, grant number NE/N018095/1]. 

Continuing this theme of work is an extension of ORCHESTRA, called ENCORE, which will run for a year from April 2021 to March 2022.