The surface ocean is home to billions of microscopic plants called phytoplankton which produce organic matter in the surface ocean using sunlight and carbon dioxide. When they die they sink, taking this carbon into the deep ocean, where it is stored on timescales of hundreds to thousands of years, which helps keep our climate the way it is today. The size of the effect they have on our climate is linked to how deep they sink before they dissolve - the deeper they sink, the more carbon is stored. This sinking carbon also provides food to the animals living in the ocean's deep, dark 'twilight zone'. Computer models can help us predict how future changes in greenhouse gas emissions might change this ocean carbon store. Current models however struggle with making these predictions. This is partly because until recently we haven't even been able to answer the basic question 'Is there enough food for all the animals living in the twilight zone?'. But in a breakthrough this year we used new technology and new theory to show that there is indeed enough food. So now we can move on to asking what controls how deep the carbon sinks. There are lots of factors which might affect how deep the material sinks but at the moment we can't be sure which ones are important. In this project we will make oceanographic expeditions to two different places to test how these different factors affect carbon storage in the deep ocean. We will measure the carbon sinking into the twilight zone and the biological processes going on within it. Then we will determine if the systems are balanced - in other words, what goes in, should come out again. We will then write equations linking all the parts of the system together and analyse them to make them more simple. At the same time we will test whether the simple equations are still useful by seeing if they produce good global maps of ocean properties for which we have lots of data. Finally, when we are happy that our new equations are doing a good job we will use them in a computer model to predict the future store of carbon in the ocean.