Here are some uses of ocean :

Food: fish and other hardshelled animals 
Traveling: getting to one place to another/tunnels,ships 
Swimming:recreational purposes. 
Mining for various fuel (oil) and minerals, 
Storing carbon dixide emissions in specialized tanks in places like the norweigian sea. 
Oceanographers study the sea, we learn alot through tectonics plates .

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Oceans soo big when compared to revers ,ponds,lakes etc.,From oceans we get salt ,fishes,Pearl's and many food items. fisherman depends upon oceans. Many of the acuatic animals also depends upon oceans
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