The biological carbon pump is one route to transfer carbon from the surface ocean into the deep ocean. Without the pump, atmospheric CO2 levels would be ~ 50 % higher than they already are. Despite its importance, we currently struggle to understand how the efficiency of the biological carbon pump varies over time – whether on scales of days, seasons or years. This makes it difficult to determine the biological processes controlling the pump, and therefore to model it. As a result, our understanding of how this important part of the global carbon cycle might respond to climate change is poor. In this talk I’ll discuss four questions: How big is variability in the biological carbon pump over time? How does this affect our understanding of the biological carbon pump? Can variability tell us something useful about the processes driving the biological carbon pump? How can new technologies help us to quantify variability in the biological carbon pump?