Vertical motions play a key role in primary production in the upper ocean, as they transport nutrients that phytoplankton need to grow. Until recently, scientists believed that three main types of dynamics dominated vertical motions in the upper ocean: mesoscale geostrophic eddies at horizontal scales on the order of 10–100 kilometers, internal waves with horizontal scales on the order of 0.1–10 kilometers, and microscale turbulence on scales of 0.01 kilometers or less. Now, scientists are beginning to realize the importance a fourth type of dynamics: submesoscale dynamics near the ocean surface. Submesoscale dynamics have horizontal scales on the order of 1–10 kilometers, vertical scales on the order of 100 meters, and time scales on the order of 1 day. Submesoscale dynamics arise through advective interactions that involve mesoscale currents and are influenced by Earth's rotation and the ocean's density stratification.