海洋
hǎiyáng · HSK 6
ocean
🌊 海 sea + 洋 ocean = the vast open sea
海 already means sea, and 洋 means ocean or vast. Together they reinforce each other into the full concept of the ocean — deep, briny, profound. Think of it as 'sea-ocean,' doubling down on boundless saltwater.
海 — water radical 氵 + 每 (phonetic)
海 is a phono-semantic compound. The 氵 (water) radical signals the meaning—a vast body of water—while 每 supplies the sound. Originally referring to the sea or ocean, it later extended figuratively to mean 'vast' or 'a great quantity,' as in 人海 (a sea of people).
洋 — water radical 氵 + sheep 羊
洋 combines the water radical 氵 (meaning) with 羊 'sheep' (phonetic, hinting at the sound yáng). Originally it referred to a vast body of water or ocean. Later it extended to mean 'foreign' or 'overseas,' since foreign things came across the ocean.