Currents play a huge role in marine productivity, through a process called upwelling. Sea life is concentrated in the sunlit waters near the surface, but most organic matter is far below, in deep waters and on the seafloor. When currents upwell, or flow up to the surface from beneath, they sweep vital nutrients back to where they're needed most. Nowhere is the link between ocean circulation and productivity more evident than around Antarctica. There, strong currents pump nitrogen and phosphate up from the deep sea to fuel vast blooms of algae and other plants. These plankton are eaten by swarms of shrimp-like crustaceans called krill. Because of upwelling nutrients, krill are abundant enough to feed the largest animals on earth, baleen whales, as well as myriad penguins, seals, and seabirds.