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The University of Southampton

New project to reveal the secrets of the ocean’s ‘twilight’ zone

Published: 20 May 2015

The University of Southampton is to share in a £3.7m grant to investigate the ocean’s ‘twilight’ zone, which plays a key role in storing carbon to keep atmospheric CO2 30 per cent lower than it would otherwise be.

This twilight zone is the part of the ocean between 100m and 1000m below the surface of the sea, where a small amount of light from the sun can still penetrate. It is currently known that the efficiency of carbon transport from the atmosphere through this zone has an impact on atmospheric composition. However, it is not known what factors affect this efficiency.

The project, led by the National Oceanography Centre (NOC) is called COMICS – Controls over Ocean Mesopelagic Interior Carbon Storage – and it will build the first model of carbon transport in the twilight zone based on direct ecological measurements. By 2020, once this project is complete, COMICS will have helped make predictions of climate change more accurate.

The COMICS project will use a new methodology to make more accurate and direct measurements of carbon transport. It will involve comparing the amount of carbon entering the twilight zone (taken from samples of the sediment that sinks, often referred to as ‘marine snow’ owing to their appearance as they fall down through the ocean) with the amount of carbon consumed by biological processes within the system, calculated by measuring the rate that microbes and animals, such as jellyfish and krill, breathe.

The lead University of Southampton investigator on the project, Dr Phyllis Lam , is particularly interested in what tiny microscopic organisms do in the marine snow. She said: “These marine snow particles are major vehicles for carbon delivery into ocean interior and they are teaming with diverse microscopic life – the major recyclers in the ocean. However, these tiny microbes don’t just sit there; they feed on the available carbon, where some can break the marine snow apart, while others glue pieces together, some release nutrients from the snow while others make new food-like plants that are not dependent on sunlight. In other words, these microbes can substantially change the size and composition of marine snow and, in turn, carbon export. To what degree and in which direction, however, we have yet to find out.”

Once COMICS has built an understanding of how the twilight zone works, a simple mathematical model of the zone will be created and used in larger global environmental models. Dr Mark Moore , also from the University of Southampton, added: “COMICS represents a fantastic opportunity to bring together multiple organisations and approaches in tackling a key problem in our understanding of the oceanic carbon cycle."

COMICS has received funding from the National Environmental Research Council (NERC) and is a collaboration between the universities of Southampton, Queen Mary London, Liverpool and Oxford, NOC and the British Antarctic Survey.

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