Oceanographer Dr Matthew Humphreys investigates the chemistry of the marine carbon cycle and CO2exchange between the atmosphere and ocean. ‘The ocean absorbs about a quarter of the CO2 we emit each year, reducing the rate of human-driven climate change. But there is a drawback: absorbing extra CO2changes the chemistry of seawater, for example lowering its pH, which is known as ocean acidification. My research focuses on understanding the balance of the equilibrium chemical reactions involved. How do these equilibria in the ocean control the exchange of CO2? And what is the role of biological processes, such as the cycle of plankton growing in the sunlit surface ocean and sinking after they die, which can transport carbon down into the deep sea?’