Scientists unravel the fast-moving ‘butterfly effect’ of the deep ocean | University of Cambridge

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Scientists unravel the fast-moving ‘butterfly effect’ of the deep ocean

Tiny, invisible swirls and twirls – not much bigger than a coin – deep below the ocean’s surface are silently shaping some of the biggest forces steering our climate: sea level rise, fisheries collapse, extreme flooding, and how much carbon dioxide the ocean absorbs.

An international research team, led by the University of Cambridge, found that deep ocean turbulence – the process that distributes heat, nutrients and carbon from the surface to the seafloor and back – affects our lives not on a scale of thousands of years as was previously thought, but within the span of a human lifetime.<br>However, the tools used to predict these effects and inform policy do not adequately represent this turbulence, or the speed at which it moves. The results are reported in the journal Nature Communications.<br>The findings come at a time when global ocean research of this kind is at risk. In May, the US National Science Foundation announced the dismantling of the Ocean Observatories Initiative, a $368 million ocean observation network that provides vital oceanographic data worldwide, although the plans were later reversed.<br>Changing turbulence patterns could affect our climate in tangible ways, which is why this type of ocean monitoring is key: if nutrients are not being pulled from the deep ocean to the surface, it could cause marine food chains to break down, which would in turn cause fisheries to collapse. The way that heat is transferred from the deep ocean to shallower waters and back affects how Arctic and Antarctic ice melts, which affects sea level rise, storm intensity and flooding levels.<br>Using a combination of previously collected physical and chemical measurements, the researchers identified several fast-moving climatic processes affected by small-scale turbulence, including the distribution of heat, nutrients, and carbon. When compared with how climate models predict how turbulence in the deep ocean will affect life on land, the researchers found these models require significant improvements.<br>“There is a microphysics of the ocean, similar to cloud physics, that is extremely difficult and expensive to observe, but it governs our lives on human-relevant timescales — from ocean circulation changes to ecosystem dynamics, with implications for fisheries and food security, to coastal flooding and heatwaves,” said lead author Dr Laura Cimoli from Cambridge’s Department of Applied Mathematics and Theoretical Physics (DAMTP). “We need the tools we use to predict these effects to be as accurate as possible, and we found that’s currently not the case.”<br>“If I think about what matters most on human timescales, it's three things: marine nutrients and ecosystems, which impact food security; Arctic changes, which have direct geopolitical implications and almost immediately affect extreme weather and flooding in the UK; and mixing of the deep southward flows feeding warm water to Antarctic ice shelves, which drive sea level rise,” said co-author Dr Ali Mashayek from Cambridge’s Department of Earth Sciences.<br>One of the tracers the researchers used to test the accuracy of climate models was CFC (chlorofluorocarbon) concentration. CFCs were released into the atmosphere in large quantities before being banned in the 1980s under the Montreal Protocol, due to the damage they caused to the ozone layer.<br>The researchers tracked how far and how fast CFCs have travelled over the past six decades by measuring their concentration at depth. They found some deep waters have carried CFCs all the way from Antarctica to the mid-Pacific and north Indian Ocean in just 40 years. The same waters also carry carbon, oxygen, and heat. As they travel, they mix with other waters, and so turbulence is key to how much tracers,...