Jonas Ekman Fjeldstad (November 22, 1894 – February 20, 1985) was a prize-winning Norwegian oceanographer and mathematician.

He received his candidatus realium degree at the Royal Frederick University and became an assistant professor of geophysics in 1922 at the University Museum of Bergen.

[2] It was Fjeldstad that correctly assumed the existence of the Lomonosov Ridge, which divides the Arctic Ocean into two large ocean basins.

[2] To determine this, he used wave data collected by Harald Sverdrup.

Fjeldstad continued studying waves for his doctoral degree in 1930, and he developed a general theory of how the ocean's internal waves behave (published as Interne Wellen, Internal Waves, 1933).