How do we know when the Atlantic ocean ends and the Pacific begins? --- Ashish, Bangalore, India
Marshall Brain Answers:
If you look at a map of the world like this...
...You can see that there are three big oceans: The Pacific, the Atlantic and the Indian oceans. Down near Antarctica there could be some confusion over where one ocean ends and the next begins, so by international agreement there are geographic dividing lines. As this article explains:
The boundaries between the oceans are based on geographic criteria and have little to do with physical water-mass boundaries. The Atlantic is separated from the Indian Ocean by the 20° E meridian, and from the Pacific Ocean (in the south) by a line extending from Cape Horn at the tip of South America to the South Shetland Islands off Antarctica's tip and (in the north) by the narrowest part of the Bering Strait. The dividing line between the Pacific and Indian oceans extends along an arc through the Malay Peninsula, Sumatra, Java, and Timor to Cape Londonderry in Australia, to Tasmania, and then along the 147° E meridian to Antarctica.
So there is an arbitrary dividing line drawn between the tip of South America and the islands you can see off Antarctica in the map below:
There is another connector between the Atlantic and Pacific at the Panama Canal, described here: