Scientists studying the carbon sequestration cycle of the ocean have looked at micro-organisms in the ocean’s depths that consume phytoplankton falling dead from higher up that have consumed carbon. When the 500 micron small phaeodarians eat the dead carbon-rich stuff falling their way the carbon never makes it to the seafloor. Instead it has the potential to remain an active element in the global warming cycle, I would guess, as they are consumed themselves by sea life travelling up.
Carbon is the basis for organic molecules so the idea of inventing a method of getting carbon in the ocean to bind with some artificially added molecule to sink to the sea floor to stay out of the way for hundreds or thousands of years is dicey.
The ocean surface to a few hundred feet has a limited ability to absorb carbon dioxide. Organic chemists as well as oceanographers may be searching not only for discovery of how the carbon cycle works in the ocean comprehensively, they may as well search for methods to increase it efficiency and capacity to absorb and process carbon dioxide out of the atmosphere.