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.
These small waves, much like the ripples caused by a stone dropped in a pond, eventually break and create turbulence and mixing. While scientists have long assumed that this deep ocean turbulence only mattered over long time scales, our new research reveals a different story. We've discovered that what happens deep below the ocean's surface can significantly influence what happens above it, even over the course of a single year.
Our study, published in Nature Communications, used a clever combination of physical and chemical measurements. We examined how chlorofluorocarbons (CFCs), once used in refrigerants and aerosols, entered the ocean and moved around the globe. By measuring CFC concentrations at depth, we calculated how long it had been since these deep waters last mixed with the surface and how quickly they moved. This gave us a window into the complex dance of heat, carbon, and nutrients between the atmosphere and ocean.
In just 40 years, some deep waters have transported CFCs from Antarctica to the mid-Pacific and north Indian Ocean. This is a remarkable feat, considering the vast distances involved. But it's not just about CFCs. We also used dyes injected into the ocean to track the movement of waters directly. One experiment, conducted in a deep canyon near the UK, showed that the dye rose towards the surface, climbing as much as 100 meters a day.
This small-scale turbulence is crucial for several reasons. Nutrients like nitrate and phosphate, the foundation of the marine food web, are pulled from the deep ocean to the surface. If this process is disrupted, entire ecosystems and global fisheries could collapse, impacting global food security. The way heat is transferred from the deep ocean to shallower waters also affects Arctic and Antarctic ice melt, which in turn influences sea level rise, storm intensity, and flooding levels worldwide.
However, global climate models have been falling short. They significantly underestimate the mixing and vertical movement of water, using simple approximations called parameterizations. This is a problem because it means we're missing a crucial piece of the puzzle. Just as clouds form due to tiny physical events with outsized impacts, deep ocean turbulence plays a significant role in climate patterns.
To improve our models, we need to update them with new parameterizations that account for our enhanced understanding of deep ocean mixing. This will make them more accurate and useful for predicting future climate scenarios. While observing small-scale mixing is still challenging, we've made significant progress in the past decade. Regional and global observation programs, coupled with advancements in high-performance computing, have rapidly improved our understanding of mixing and its impacts.
However, we still face obstacles in fully unraveling the complex relationship between deep ocean turbulence and climate. As mixing observations remain rare, we must find innovative ways to overcome this bottleneck and allocate resources strategically to accelerate progress. The ocean's deep currents are a powerful force, and it's time we harness their potential to better understand and protect our planet.
