Is it zero degrees or zero degree?

Atlantic Ocean

It is the South Atlantic Ocean off Sao Tome and Principe.

That point is in the Gulf of Guinea off the coast of West Africa, about 300 miles south of Accra, Ghana. We missed today's local conditions and forecast, but being on the equator and at sea, you can...

90 degrees south latitude and ANY longitude is the South Pole.

Where the Equator and the Greenwich meridian intersect. This point of intersection is not on land, it is in the Atlantic Ocean in the gulf of Guinea.