Over the past three billion years, primary productivity and the biogeochemical cycling of nutrients through the world’s oceans has had a profound influence over global climate. Through photosynthetic carbon fixation, marine phytoplankton not only oxygenate the planet but play a crucial role in the “biological pump”. This describes the process where dissolved inorganic materials in the surface ocean, e.g dissolved inorganic carbon (DIC), nitrate (NO3), and phosphate (PO4), are fixed as organic matter and export from the surface layer as sinking particulates. A cascade of nutrient cycling and remineralization pathways are initiated as the downward flux of particulates dissolves, is grazed upon by zooplankton, or is subject to bacterial hydrolysis (See Figure below). The disequilibrium gradient created at the air-sea interface modulates CO2 drawdown, and while most of the particulates don’t make it to the sea floor, those that do provide a food source for deep sea organisms i.e coral!, or form deep sea sediments sequestering carbon over geological timescales.

The Biological Pump, taken from Chisolm et al., 2000 (Nature)