The ocean water will freeze if the temperature is cold enough (below 32 degrees). For example, there are a lot of icebergs and ice in both poles on our planet Earth. So why does the ocean near us or in most places are not freezing?

One very important fact is that we are receiving sunlight all the time (more sunlight here than both poles). It will keep the ocean water warm and above the freezing point. The water deep in the ocean can not receive the sunlight, so it is colder (about 40 degrees) than the water near the surface of the ocean (about 70 degrees as a typical example). But it is still above the freezing point of water and will not freeze.

There are two other facts that keep the ocean water from freezing. The first one is the motion of the ocean water. You know that the ocean water near the surface is moving, it will make it a little bit harder for the water to freeze. The other important factor is the large volume of the ocean water . About 70% of our planet is covered by the ocean, and the deepest place in the ocean is even deeper than our highest mountain. The large volume of the ocean plus the motion will make it difficult to lower the average temperature of the ocean water. During the daytime, the ocean will receive the sunlight, the water near the surface will be warmer, and it will transfer the heat to the deep water and keep it from further lowering the temperature. During the night, the air near the surface of the ocean can be freezing (not here, but it can happen in other places), but the deep water is slightly warmer than the water near the surface, so it will keep the water near the surface from freezing.

So basically it is mostly a combination of these three factors that keep the ocean water from freezing. Now you can understand a lot of phenomena related with water freezing. Those places receiving less sunlight will have a higher chance of water freezing. That's why we don't even see snow here. At the same place say in Boston during the winter, you will probably found a small pond with all of the water freezing during the night, while the water in a nearby big river is still running (not freezing).