Some of the two-way interactions between ocean biota and climate are mediated by biogeochemical cycles that link the different components of the climate system. As suggested by proxy records extracted from ice and ocean cores, by recent measurements, and by numerical models, such two-way interactions were likely major players in past climate variability on glacial-interglacial timescales, and may act to amplify or moderate an anthropogenically induced climate change in the near future. At present, our lack of understanding of these interactions hampers our ability to anticipate the consequences of possible anthropogenic climate change. In this article, we highlight some of the possible feedbacks between ocean biota and climate, reviewing some key biogeochemical processes and discussing mechanisms of two-way interactions. We also outline the need and strategies for continuing research aimed at advancing our understanding of these feedbacks and discuss their significance.