The supply of iron from shelf sediments to the ocean

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Phytoplankton (microscopic algae) lie at the base of the marine food chain, so their presence is essential for sustaining higher organisms such as fish. They also take up as much atmospheric carbon dioxide as land plants and in doing so, help regulate the global climate. Iron is among the most important nutrients required by phytoplankton to grow and is used in vital biological functions, including photosynthesis (conversion of carbon dioxide and water into glucose and oxygen). Iron is abundant on land and in surrounding shallow coastal waters, known as 'shelf regions'. In contrast, iron is present at very low concentrations (less than 1 iron atom to every billion water molecules) in the deep open ocean, far from land. This means that the growth of phytoplankton can be restricted due to the lack of iron. Iron is lost as it is transported from the coast to the open ocean because of its chemistry - it is very insoluble in seawater. However, a small amount of iron from coastal regions does reach the open ocean and this iron makes up a large portion of the new iron supplied to the phytoplankton growing there. Studies of marine iron chemistry require us to determine how much iron there is, what chemical forms iron is in (e.g. dissolved forms or particles) and the changes that occur between these various forms. The amounts of these different forms change depending on the time of year, the location of the water, the number of particles and the organic molecules in seawater. Sampling and measurement of iron at very low concentrations in seawater is challenging and the applicants are among the few research groups in the world who are able to do this reliably.In this project we address the question of how currents, tides, weather and marine iron chemistry allow new iron to be transported away from the shallow shelf waters around the UK, to the nearby open ocean. The project will ultimately allow us to address the broader question of how the amount and chemical form of iron in coastal waters and shelf sediments can influence phytoplankton growth in the open ocean. Furthermore, the impact of human activity and climate change on the transport of iron from the UK shelf region is poorly understood. This is important because changing ocean productivity by changing iron supply to the open ocean will also alter the amount of carbon dioxide taken up by phytoplankton.