A question from drifting ice
Nansen observed Arctic ice drifting at an angle to the wind, and Bjerknes asked Ekman to investigate. In Ekman’s wind-current model, friction transmits wind forcing downward while Earth’s rotation changes current direction with depth, producing the Ekman spiral.
Explaining dead water
Ekman also investigated unusual resistance to ships moving through layered water. When lighter fresh water overlies denser seawater, a moving vessel can generate internal waves at their interface, losing energy and slowing down without equally conspicuous surface waves.
References: [1]
Theory, instruments and teaching
After his doctorate in 1902, he worked at the oceanographic laboratory in Kristiania, designed current-measuring instruments and joined sea investigations. He was professor of mechanics and mathematical physics at Lund from 1910 to 1939, also writing a long-used mechanics textbook.
References: [1]