Whales can be deep divers, going to the depth of the ocean where nutrients are found, and carrying them up to the nutrient-poor surface when they swim up to breathe. At the surface, different algae types use the nutrients for consumption, making their population grow, and by that create more photosynthesis, which turns CO2 into oxygen.
Photo by: https://commons.wikimedia.org/wiki/File:Mother_and_baby_sperm_whale.jpg
