The equator
The Atlantic is east of North America. It is the ocean that separates the American continent, north & south, from Europe & Africa.
There is no circle called the Atlantic circle. The Arctic and Antarctic circles are north and south of the equator respectively
Do you mean the Arctic Circle? If so, it is north of the equator. Far North. I have not heard of an Atlantic Circle. There is a North Atlantic and South Atlantic Ocean.
The part of the Atlantic Ocean above or North of the Equator.