In this video, Dr Stephanie Henson explores why it is so important to monitor phytoplankton distribution from space using the technique of ‘ocean colour’ remote sensing, and provides an overview of how this is achieved using satellite technology. Dr Henson briefly introduces some of the key challenges associated with the measurement of ocean colour, and looks ahead to the use of new hyperspectral sensing systems, which are expected to dramatically increase the detail with which we are able to study ocean phytoplankton.

Phytoplankton are microscopic organisms similar to terrestrial plants, in the sense that they use chlorophyll pigments in the process of photosynthesis. There are thousands of phytoplankton species which live in massive abundance in the surface layers of the open ocean, and they provide a direct food source to creatures ranging from animal-like zooplankton to whales. They are the foundation of the aquatic food web, sustaining almost everything else that lives in the oceans, including our fisheries.

As with terrestrial plants, during photosynthesis phytoplankton absorb carbon dioxide (CO₂), and so they significantly increase the oceans ability to sequester (CO₂). Phytoplankton therefore help protect our atmosphere from the full extent of our anthropogenic greenhouse gas emissions, and are estimated to absorb around 50 billion tonnes of carbon every year. As well as sunlight, phytoplankton require nutrients to grow, and their distribution in different regions of the ocean can change dramatically across location and time.

Using satellites to measure ocean colour is one of the most effective ways of assessing and monitoring phytoplankton distribution. Although we cannot see the microscopic phytoplankton themselves, their huge abundances and chlorophyll content can change the appearance of the ocean water, and these colour variations can be observed from space. Satellite ocean colour data therefore provides essential information on the state, variability and seasonal cycle of phytoplankton populations, vital for advancing our understanding of their role in the Earth system.

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• Dr Stephanie Henson

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