Is there a possibility that Deuterium abundant below the deepest ocean, like Pacific Ocean?

This is because Deuterium is the best source of Hydrogen (the fuel of the future) and avoid pollution and green house effect.

Any water is a source of hydrogen but it is expensive to make and hard to store.

Deutertium is an isotope of hydrogen that has a neutron in its nucleus (regular hydrogen, or protium, has no neutrons)

Because of the additional particle, deuterium is twice as heavy s regular hydrogen. Water molecules with deuterium are therefore heavier than regular water molecules, and should ik to the otom of a mixture of both. Oceans, therefore, could have plenty of deuterium near the bottom.

However, contrary to what you are saying, deuterium is not a source of hydrogen, but a form of it. Since you are referring to hydrogen as a fuel, it would not really matter if you use protium or deuterium for fuel.

Nevertheless, deuterium is the isotope that is extremely useful when it comes to nuclear fusion reactions, since the added mass will mke interactions between nuclei more probable than with protium nuclei.