The most public threat is whaling. There are many more threats that are not as well known. Many of these threats are seriously harming populations of whales and dolphins around the world.
Some animals have to endure many threats at once.
It cycles water from the surface to the ocean floor over thousands of years. It might trigger a 'domino effect' of marine ecosystem collapse around the world. This same system also absorbs large amounts of carbon dioxide. Some believe it rivals large rainforests and the 'lungs of the earth'. If it is altered the effect may be to allow more carbon dioxide into the atmosphere.