Every winter, storms and swirling currents in the Labrador Sea shove surface plankton—and the carbon they contain—straight down into the deep ocean, bypassing the slow process of sinking dead matter. This matters because the ocean’s “biological carbon pump” has long been treated as a purely biological process: plankton die, sink, and store carbon for centuries. But recent evidence suggests that physical ocean mixing—from storms, winter cooling, and meandering currents—may drive as much carbon to depth as sinking alone. The two fields have worked in isolation, and the stormy North Atlantic is nearly impossible to sample from ships. ReBELS will use autonomous underwater robots to measure both biological particles and physical transport simultaneously over a full year in the Labrador Sea, where stored carbon lingers for over 1,000 years. If successful, the project will produce the first integrated, year-round dataset of how biology and physics together move carbon into the deep ocean. This is fundamental science: it will not directly change a weather forecast or a shipping route. But the results will feed directly into climate models, which currently lack this coupling. Better models mean more reliable projections of how the ocean’s carbon storage will respond to warming and melting ice—a system that quietly keeps the planet’s climate stable.
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The surface ocean is home to billions of microscopic plant-like phytoplankton which produce organic matter in the surface ocean using sunlight and carbon dioxide. When they die, they sink and take this carbon into the deep ocean, where it is stored on timescales of hundreds to thousands of years. This storage helps to keep our climate the way it is today. This process of biological CO2 uptake and storage in the deep ocean is called the 'biological carbon pump' and, in order to understand how our climate will change in the near future, we need to understand what controls this process. Until fairly recently, the biological carbon pump was thought to work almost independently from the mixing processes that occur in the oceans, such as during storms, winter or by meandering ocean currents. However, recent work suggested that these physical processes may be very important for the biological carbon pump, providing a direct pathway for carbon to reach the deep ocean, and can contribute as much carbon to depth as the sinking of dead matter alone. Therefore, we urgently need to understand how the biological and physical processes interact to transport organic matter into the deep ocean. Two reasons explain this clear oversight: Physical and biological oceanographers often work independently, so that crossdisciplinary processes can get overlooked. In addition, the location where, and times when, these processes have the most dramatic effect on ocean carbon storage are hostile environments to work in, with very high waves and strong winds that make working from ships nearly impossible. ReBELS is an exciting programme that will bring together physical and biological oceanographers to closely work together on the biological carbon pump. To overcome the logistical challenges, ReBELS will take advantage of the recent developments in technology, using state-of-the-art marine autonomous robots that will be able to sample the ocean at times where we cannot do so with ships. Our study site will be the Labrador Sea in the Northwest Atlantic. There, organic carbon stays in the deep ocean much longer than anywhere else in the world (>1000 years). Moreover, the Labrador Sea has been identified as a very important location for the climate, as it is strongly affected by increasing temperatures and melting ice. Using autonomous technology, we will measure the biological carbon pump over the course of an entire year, and quantify carbon transport and carbon storage through the different biological and physical processes. To do so, we will measure the distribution of organic matter particles throughout the water column and determine whether they are sinking or being transported by ocean mixing. We will then extend our results to the entire Northwest Atlantic using proxies that can be determined on larger scales (for example from satellites). Finally, we will work with modellers to include these important processes when predicting climate in the future.
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