Question

What causes upwelling in oceans?

Answer 1

Wind.

Explanation:

The ocean basically works like a giant bathtub. If you fill up a bathtub and put a very strong fan on one side, the top layer of water is going to flow to the other side. That means the bottom layer is constantly flowing upward to fill in the top layer that's being blown away.

Wind blows the top layer of ocean water away, allowing the bottom layer to float upward.