A £2.5 million project to transform our understanding of how the ocean breathes by storing greenhouse gases from the atmosphere is now underway with the aim of providing our most in-depth understanding of ocean mixing to date.

Led by the University of Southampton and the National Oceanography Centre (NOC), the project intends to deliver detail to such “unprecedented” levels that it will mark the dawn of a new era for ocean-focused climate prediction models.

Called REMIX-TUNE, the project has been awarded £2.5 million from the European Research Council to deploy a cutting-edge fleet of sensors on board high-tech floats across the ocean, through which they will receive a new level of detailed data on how the ocean breathes.

It’s through a vital process known as mixing – the tiny turbulent movements that pull water, heat, and chemicals from its surface down into the deep – that the ocean ‘breathes’. And it’s this ventilation that helps to regulate the Earth’s climate, buffering against the impacts of human-induced climate change.

Mixing also plays a key role in regulating ocean current systems, such as the Atlantic Meridional Overturning Circulation (AMOC) which has been the recent focus of much concern among the scientific community for running perilously close collapse, if not already heading – with no degree of uncertainty – towards it.

“Small-scale mixing plays a crucial role in how the ocean exchanges carbon and heat with the atmosphere and stores it below the surface,” said Dr Bieito Fernandez Castro, a lecturer in physical oceanography at the University of Southampton, leading the project.

“Yet, much about this crucial process remains a mystery, so there’s a higher degree of uncertainty in our estimates that we’d like. It happens on such small scales (ranging from centimetres to kilometres) that it has been hard to measure, meaning current ocean and climate models fail to capture the intricate dynamics at work.”

The REMIX-TUNE project will deploy these ocean-data collecting buoys in key regions of deep water formation where much of the heat and carbon sequestration takes place – namely, the North Atlantic and Southern Ocean.

Equipped with turbulence sensors and onboard computers, the floats will pass through the water column from the surface down to depths of up to two thousand metres and back up again over several years, capturing detailed data on how water mixes at both the mesoscale (large eddies) and micro-scale (tiny, chaotic swirls).

The floats themselves are similar to those used since the 2000s when they were put to work measuring the temperature and salinity of the ocean, as well as other properties to help with forecasting and modelling. Until now, however, the technology wasn’t available to enable them to observe ocean mixing.

“It’s exciting to deploy them in significant numbers for this purpose,” said Dr Castro. 

The data captured will generate the first comprehensive, observation-based global database measuring mixing’s role in ocean ventilation. This detailed understanding will then feed into the next generation of climate models, improving their ability to simulate the ocean’s role in storing heat and greenhouse gases.

“Combining the new data with existing hydrographic profiles from the global Argo programme, we can reconstruct mixing over the past 25 years over the global ocean to provide much more accurate mixing estimates,” said Dr Alex Megann at the National Oceanography Centre.

“We’ll then use a model called NEMO, which is the ocean component of the UK’s contribution to the Intergovernmental Panel on Climate Change (IPCC), to use our improved estimates of mixing to give a much clearer picture of how ocean ventilation regulates our climate.”

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