The temperature of ocean water affects the climate of nearby land. Land is warmed quickly by the sun. Ocean water is not warmed as quickly. Air above the water is cooler than air above the land. The land is cooled as the cool air over the ocean moves inland.
Ocean water stays warm for a long time, once it is heated.
The air above the water stays warm also. In winter, warm air over the ocean moves inland. The air keeps the land warm. The ocean is also part of the water cycle. The sun's heat evaporates ocean water.