Yup! Deliberately fostering phytoplankton growth using "iron fertilization" even has its own Wikipedia article [1]. The idea is that iron, not nutrients, is a limiting factor to phytoplankton growth in some areas, so we could boost phytoplankton just by throwing (a suitable form of) iron in the ocean.
IIRC, it's a controversial topic because the lack of a unified regulatory body for oceans makes experimentation difficult, and there are poorly-understood side effects with various algae. Also, wholesale manipulation of an ecosystem for scientific purposes is usually frowned upon (pollution, though, seems to get along just fine...).