Learning how water is mixed by currents and other means is essential in understanding how heat energy, nutrients and gases move between Earth’s water bodies, landmasses and atmosphere. The ocean has an interconnected current, a circulation system powered by wind, tides, Earth’s rotation (Coriolis effect), the sun (solar energy) and water density differences. Ocean water circulation affects temperature extremes, local weather conditions, global climate patterns, and the cycling of gases and nutrients in marine ecosystems.

To better understand the impact ocean mixing and currents have on global climate and physical processes in the ocean, scientists create climate and circulation models. Scientific models are used to explain or predict a system that is hard to observe. Many factors must be considered when creating a scientific model. In the case of ocean mixing and circulation, winds, tides, and currents are the dominant forces considered. Some scientists argue that other, less-studied sources of mixing, including swimming animals at mid-water depths, should also be factored into the models to obtain more accurate predictions.

National Geographic Explorer Kakani Katija is a scientist who studies the impact swimming animals have on ocean mixing and circulation. As a bioengineer, Katija applies engineering principles to the study of marine biology. She works with oceanographers to explore how the movement of fish, jellies, whales and plankton mixes water under the surface of the ocean. She and her team want to show that small forces, like many swimming jellies, can add up to a large force resulting in ocean mixing. The idea that a small organism can have a large effect on a physical system is often referred to as the butterfly effect. If Katija’s theory is confirmed, it could change our understanding of ocean circulation and influence future global climate models.

Katija’s research includes field and lab studies, as well as new methods and technologies she has developed to help with her research. In one method, scuba divers use a camera and high-powered laser to illuminate and measure the movement of particles in the water around the moving animals. In another method, dye is released into the water around a swimming organism. The dye can be used to measure the direction and movement of water swirling around and dragging behind the animal. Data show that the amount of mixing depends on the animal’s size, shape, movement type and direction, and distance traveled. Results from these research methods indicate deeper, calmer waters can be mixed more easily with less energy input from the animal.

Many different forces and processes affect ocean mixing, both on the surface and at depth. Scientists hope to investigate the impact that biological processes, including swimming animals and the resulting butterfly effect, may have on ocean circulation. When combined, these forces and processes drive the ocean’s global circulation system, playing a key role in distributing heat energy, regulating weather and climate, and cycling vital nutrients and gases.