The systematic study of our oceans along the with first instrumental observations started around 150 years ago. To study changes that occurred before this, and to better understand the long-term functioning of the ocean, geological records such as ocean sediments are investigated. This field of research is called ‘paleoceanography’. In this talk, I will introduce some of the basic concepts, methods, and research questions that underlie paleoceanography. In particular, I will focus on patterns of ocean (and climate) variability of the past 2.5 million years – the time period when the growth and decay of large ice sheets dictated Earth’s climate. Finally, I will discuss some case studies that highlight the importance of warm ocean currents and their influence on the melting of ice in the Arctic.