To combat rising temperatures, we must decrease CO2 levels on a global scale. Examining all our options, including using the oceans as a CO2 sink, gives us the best chance of cooling the planet. Phytoplankton, the photosynthesizing variety of microorganisms that float on the ocean’s surface, are one of the main components of the carbon cycle’s biological pump that takes CO2 out of the air to store in the ocean’s depths. The tiny organisms need minerals like iron to grow and multiply, but there’s only a fixed amount floating at the surface of the waters with them, which limits how much phytoplankton can bloom. So just as fertilizer can help photosynthesizing organisms flourish on land, the same help could – theoretically – be offered to the sunlight eaters that float on our seas. Whales once performed a huge chunk of natural ocean fertilization, feeding plankton the otherwise out-of-reach nutrients via giant plumes of poop. Before industrial whaling drastically diminished whale numbers, whales helped remove close to 2 million tonnes of carbon dioxide a year through this process; now it’s closer to 200,000 tonnes. So by artificially adding this missing fertilizer, we could stimulate these microbes to grow and reproduce, suck up more CO2 from the air, and carry it with them to their deaths. 

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