Thousands of metres below the ocean’s surface, there are tiny waves moving through the water.
Much like breaking waves at the beach, these small waves within the ocean must eventually break. When they do, they create turbulence and mixing, similar to what you feel from a big wave breaking on the beach.
This might seem far removed from your everyday life. In fact, for a long time scientists have assumed this deep ocean turbulence only mattered over long time scales – that is, centuries to millennia.
But our new research, published in Nature Communications, shows this isn’t always the case. In fact, what happens deep below the ocean’s surface can change what happens above it – even over the course of a single year.
Yet the tools scientists use to understand how the climate is changing do not currently consider the effects of these tiny, crucial movements.
Studying different scales
For our study, we used a combination of previously collected physical and chemical measurements to examine the many different scales on which deep ocean turbulence shapes the global climate system, with a particular focus on short timescale impacts.
Chlorofluorocarbons (CFCs), chemicals once used in refrigerants and aerosols before being banned in the 1980s, entered the ocean from the atmosphere at a known time and rate. Because CFCs don’t occur naturally in seawater, their presence in the ocean is only possible through contact with the atmosphere and subsequent transport by ocean currents and mixing.
By measuring CFC concentrations at depth today, we can calculate how much time has elapsed since these deep waters last mixed with the surface, and how quickly they moved around the globe. In turn, this gives us a better understanding of how heat, carbon and nutrients are transferred between the atmosphere and ocean, and how they are transported.
In just 40 years, some deep waters have transported CFCs from Antarctica to the mid-Pacific and north Indian Ocean.
More targeted experiments used a dye, physically injected into the ocean at a known location and depth, to track the transport and movement of ocean waters directly.
In one such experiment, dye was injected into a deep canyon in the Rockall Trough, near the United Kingdom. Rather than simply dispersing as expected, the dye rose towards the ocean surface, climbing as much as 100 metres a day.
A missing piece of the puzzle
Understanding this small-scale turbulence is crucial for several reasons.
For one, nutrients such as nitrate and phosphate underpin the marine food web. And if they’re not getting pu
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