First of all, most of the oceans are one. The Atlantic and Pacific are connected and therefore they are like one ocean; inland seas are separate. But I want to tell you this: even the oceans themselves have different climates, and different inhabitants. And the purpose is, Hakadosh Baruch Hu wanted His world to be a department store from which nothing is lacking.
The world is supplied with every kind of marine animal, like it has almost every kind of land animal, and all these help to complete the perfection of Hashem's creation. When people see so many things, especially so many different kinds of fishes, like Rashi says in Mesechta Rosh Hashana (Daf 31.) when you see so many kinds of different fishes, on the fifth day we say Harninu, make song to Hashem.
Why make song on the fifth day? Because He created fish and fowl. And Rashi says, because when you see different kinds of fishes, various fishes, and various birds, you are overwhelmed by what you see. You see the greatness of Hashem's creation and you sing to Him. If you see only one kind, it's monotonous, you don't notice it. You see all kinds of birds and all kinds of fishes, it makes your mind awake, you are stirred to awareness of the greatness of Hashem, and you say Harninu. Sing to Hashem.
And that's the purpose why there are different kinds of climates in the sea, because different kinds of fishes and different kinds of marine animals flourish in different parts of the sea.
Good Shabbos To All
This is transcribed from questions that were posed to Harav Miller by the audience at the Thursday night lectures.
To listen to the audio of this Q & A please dial: 201-676-3210