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The University of Southampton
Ocean and Earth Science, National Oceanography Centre Southampton

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

Published: 22 May 2015

Ocean and Earth Science at 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, keeping 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.

Until last year it appeared that the animals living in the ‘twilight’ zone required six times more carbon to survive and grow than was being supplied to them. However, scientists at the NOC revealed a new method that might bring the ‘carbon budget’ in this zone closer to balance. Professor Richard Sanders from the NOC, who is leading COMICS, said: “This was made possible by world-leading technology developed here at the NOC. The sediment traps we built enabled us to measure the amount of carbon entering the ‘twilight’ zone much closer to the surface than has been previously possible, which meant our measurements were more accurate.”

The COMICS project will use this 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 independent 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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