When an extremely cold, dry air mass moves over the ocean, it is likely to become a maritime polar (mP) or maritime tropical (mT) air mass, depending on the temperature of the ocean water.
If the ocean water is relatively warm compared to the cold air, the air mass can pick up moisture and heat, transforming into a maritime tropical air mass, which is generally warm and humid. If the ocean is cooler, the air mass may remain relatively cool and slightly more humid, potentially becoming a maritime polar air mass.
In summary, the type of air mass it becomes will largely depend on the temperature of the ocean water it moves over.