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 global climate dynamics. These waves, much like the breaking waves at the beach, create turbulence and mixing that has far-reaching consequences.
For a long time, scientists have assumed that deep ocean turbulence only mattered over long time scales, but our new research challenges this notion. 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. This is a crucial revelation, as it means that the effects of these tiny movements are not just long-term, but also immediate and impactful.
Our study, published in Nature Communications, used a combination of physical and chemical measurements to examine the various scales on which deep ocean turbulence shapes the global climate system. We focused on short-term impacts, and what we found was remarkable. Chlorofluorocarbons (CFCs), once used in refrigerants and aerosols, entered the ocean from the atmosphere at a known rate and time. By measuring CFC concentrations at depth, we could calculate how long it had been since these deep waters last mixed with the surface and how quickly they moved around the globe.
In just 40 years, some deep waters transported CFCs from Antarctica to the mid-Pacific and north Indian Ocean. This is a powerful demonstration of how these tiny waves can have a massive impact on heat, carbon, and nutrient transfer between the atmosphere and ocean. But it's not just about CFCs. We also conducted experiments using a dye, physically injected into the ocean, to track the transport and movement of ocean waters directly.
One experiment, injected into a deep canyon in the Rockall Trough, revealed that the dye rose towards the ocean surface, climbing as much as 100 meters a day. This is a critical finding because it highlights the importance of small-scale turbulence in the ocean. Nutrients like nitrate and phosphate, which underpin the marine food web, are at stake here. If they're not pulled from the deep ocean to the surface, the entire web could collapse, devastating ecosystems and global fisheries.
The implications are far-reaching. The way heat is transferred from the deep ocean to shallower waters affects Arctic and Antarctic ice melt, which in turn impacts sea level rise, storm intensity, and flooding levels worldwide. Yet, global climate models fail to capture these small-scale processes effectively. When compared to real-world measurements, these models significantly underestimate the mixing and vertical movement of water.
This is because they rely on simple approximations, known as parameterizations, to estimate the effects of small-scale processes. Many of these parameterizations date back to the 1990s, and they need an update. Climate models should incorporate new parameterizations that account for our improved understanding of deep ocean mixing. This would make them more accurate and useful for predicting our climate and making informed decisions about the future.
Observing small-scale mixing is still challenging, but we've made significant progress in 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, there are still obstacles to fully unraveling the impact of mixing on the climate.
As mixing observations remain rare, we must find ways to overcome this bottleneck and target resources to accelerate progress. The ocean's deep currents are a missing piece of the climate puzzle, and it's time we bring them into the spotlight. By doing so, we can improve our climate models and make more accurate predictions, ensuring a more sustainable future for our planet.
