The noun 海洋 (hǎiyáng) means "ocean" or "sea" and refers to large bodies of saltwater. It is a more formal or literary term compared to 海 and can be used as a modifier, as in 海洋王国 (ocean kingdom).
海洋里有很多我们还不了解的生物。
hǎiyáng lǐ yǒu hěn duō wǒmen hái bù liǎojiě de shēngwù.
There are many creatures in the ocean that we still don't understand.
他从小就对海洋充满了好奇心。
tā cóng xiǎo jiù duì hǎiyáng chōngmǎn le hàoqíxīn.
He has been full of curiosity about the ocean since he was little.
保护海洋是每个人的责任。
bǎohù hǎiyáng shì měi gè rén de zérèn.
Protecting the ocean is everyone's responsibility.