You may be thinking of the Antarctic Circle.
You may be thinking of the Antarctic Circle -- 66° 33′ 44″ S, or of 60 degrees S, which is the extent of governance by the Antarctic Treaty.
possibly latitudes
The 42nd northern latitude
Limerick is not really a coastal county. However the river Shannon flows into the Shannon Estuary, before entering the Atlantic Ocean. Part of the Shannon Esturary forms the northern boundary of county Limerick. See the related maps below.
The Cell Membrane forms the outside boundary that separates the cell from its environment.
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The northernmost point of the Antarctic continent is Prime Head at 63° 12' 48" S, 57° 18' 8" W. All land south of 60 degrees S is governed by the Antarctic Treaty. So, you could say that both 63 degrees S and 60 degrees S -- lines of latitude -- form a northern boundary of Antarctica: your choice.
the country that forms the northern boundary of the United States is Canada :)
This is the boundary with Ukraine: mountains and the river Tisa.
The sea that forms the northern boundary of Africa is the Mediterranean Sea. The countries of Morocco, Algeria, Tunisia, Libya and Egypt border it.
The Arctic Ocean
red river
No. Antarctica is the southern-most continent on earth. Parts of northern Canada are the northern-most land forms on earth.
The 42nd northern latitude
Both Chile and Argentina, close to Antarctica.
The sea that forms the northern boundary of Africa is the Mediterranean Sea. The countries of Morocco, Algeria, Tunisia, Libya and Egypt border it.
soviet union
The river Danube and the South Dobrogea.