The ocean's deep, hidden currents are having a profound impact on our climate, and it's time we pay attention. Tiny waves in the deep ocean, often overlooked, can affect the climate thousands of kilometres away, and this is a game-changer for our understanding of the planet's complex systems.
For too long, scientists have assumed that deep ocean turbulence only matters over long time scales, like centuries to millennia. But our new research, published in Nature Communications, reveals that this isn't always the case. What happens deep below the ocean's surface can significantly influence what happens above it, even over the course of a single year. This is a crucial revelation, as it highlights the need to consider these tiny, crucial movements in our climate models.
Our study used a combination of physical and chemical measurements to examine the various scales on which deep ocean turbulence shapes the global climate system, with a focus on short-term impacts. We measured chlorofluorocarbons (CFCs), chemicals once used in refrigerants and aerosols before being banned in the 1980s, to determine how much time has elapsed since deep waters last mixed with the surface and how quickly they moved around the globe. In just 40 years, some deep waters have transported CFCs from Antarctica to the mid-Pacific and north Indian Ocean, demonstrating the rapid movement of heat, carbon, and nutrients.
We also conducted more targeted experiments using a dye to track the transport and movement of ocean waters directly. In one experiment, dye was injected into a deep canyon in the Rockall Trough, near the United Kingdom, and it rose towards the ocean surface, climbing as much as 100 meters a day. This experiment highlights the importance of understanding small-scale turbulence, as it can have significant impacts on nutrient distribution, marine food webs, and global fisheries.
The way heat is transferred from the deep ocean to shallower waters and back affects Arctic and Antarctic ice melt, which in turn impacts sea level rise, storm intensity, and flooding levels worldwide. However, current global climate models significantly underestimate the mixing and vertical movement of water, as they rely on simple approximations called parameterizations. These models need to be updated to better capture the effects of small-scale processes like deep ocean turbulence.
Observing small-scale mixing is still challenging, but we've made significant progress over the past decade. Regional and global observation programs, along with advances in high-performance computing, have rapidly improved our understanding of mixing and its larger-scale impacts. However, we still face obstacles in fully unraveling the impact of mixing on the climate.
To overcome this, we need to find ways to accelerate progress by targeting resources to where they can have the most significant impact. This is a critical area of research, as it can help us better understand and predict the complex interactions between the ocean and the atmosphere, ultimately leading to more accurate climate models and informed decisions about our future.
