The ocean by and large determines the climate of our blue planet. It absorbs CO2 and heat, transports them between the poles and the tropics. Its organisms produce 50% of the oxygen on Earth. At NIOZ we study how do these processes work and how they are affected by climate change, and vice versa. We look at what the climate archive stored in the ocean sediments teaches us about the past – and how this knowledge might help us to understand and mitigate climate change.