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 waves, much like the breaking waves at the beach, create turbulence and mixing that scientists have traditionally assumed only mattered over long time scales, like centuries to millennia. But our new research, published in Nature Communications, reveals a different story. 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 finding because it means that the tools we use to understand climate change may be missing a vital piece of the puzzle. Our study, using a combination of physical and chemical measurements, examined how deep ocean turbulence shapes the global climate system, focusing on short-term impacts. We used chlorofluorocarbons (CFCs), chemicals once used in refrigerants and aerosols, as a tracer to track the movement of deep ocean waters. By measuring CFC concentrations at depth, we could calculate how much time had passed since these 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 between the atmosphere and ocean. This is a critical finding because it highlights the importance of small-scale turbulence in the ocean's mixing processes. Nutrients like nitrate and phosphate, essential for the marine food web, are pulled from the deep ocean to the surface, and 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, current global climate models struggle to capture these small-scale processes accurately. When compared to real-world measurements, these models significantly underestimate the mixing and vertical movement of water, relying on simple approximations called parameterizations. This is a problem because it means our models may be missing crucial details about how the climate is changing. The way clouds form is another example of tiny physical events with outsized impacts on the climate, and this, too, is a challenge for climate models. To improve our models, we need to update parameterizations with our improved theoretical understanding of deep ocean mixing. This will make them more accurate and useful for understanding our climate and making informed decisions about the future. Observing small-scale mixing, or the microphysics of the ocean, is still a challenge, but we've made significant progress over the past decade. Regional and global observation programs, along with advances in high-performance computing, have rapidly evolved our understanding of mixing and its larger-scale impacts. However, significant obstacles remain in fully unraveling the impact of mixing on the climate. As mixing observations are still very rare, we need to find ways to overcome this bottleneck and target resources to accelerate progress. In conclusion, the ocean's deep currents are a critical, often overlooked, part of our climate system. By paying attention to these tiny waves and their impact, we can improve our understanding of the planet's complex dynamics and make more informed decisions about the future. This is a call to action for scientists and policymakers to prioritize the study of these small-scale processes and their role in shaping our climate.
