Deep-sea Volcanoes play an important role in Southern Ocean Carbon storage

In research published on-line today in the respected international journal Nature Geoscience, Australian and French scientists have shown for the first time that hot waters exiting at hydrothermal vents around underwater volcanos are a significant source of iron to the global ocean. This is important because iron is a limiting nutrient for the microscopic plants, known as phytoplankton, that underpin all ocean foodwebs. Following pioneering work during the International Polar Year in 2008, the scientists have made the first measurements of the concentration of dissolved iron in the deep Southern Ocean at depths of up to four kilometres below the surface. These observations were compared to estimates of iron supply based on models of the transport of the trace gas helium-3 that also exits at hydrothermal vents, and for which data is available from around the world. Dr Andrew Bowie, a senior research scientist at the Antarctic Climate & Ecosystems Cooperative Research Centre (ACE CRC) in Hobart said: "This research is important because it represents the first description of the large scale deep-sea supply of iron produced from underwater volcanoes. We saw remarkable consistency between the predictions of the model and observations from the ocean. Now we can assess the relative significance of this deep iron source in comparison to iron supplied at the surface by dusts and sediments, including how this affects phytoplankton and thus carbon storage in the Southern Ocean". The lead author of the paper, Dr Alessandro Tagliabue, said from his Paris laboratory, "Our findings indicate that iron supplied by deep-sea volcanos is relatively constant over millennial timescales and, more importantly, helps produce between 5 and 15% of the total Southern Ocean carbon storage". "Change in the delivery of iron is likely to be the single largest forcing of Southern Ocean ecosystem health in the next century, and it is intrinsically linked with changes in climate. This research provides another piece in the climate science puzzle and is another important step in understanding the processes moderating carbon storage by the ocean", Dr Bowie said. The "biological pump" removes carbon from the atmosphere: The world’s oceans remove about 20-25% of the atmospheric carbon dioxide produced by human activities. The Southern Ocean around Antarctica plays a key role in this global carbon storage. The ability of the Southern Ocean to store carbon is driven by the growth of single-celled microscopic plants called phytoplankton, which absorb carbon dioxide from the atmosphere at the ocean surface and, when they are eaten or die and sink, transfer this carbon deep within the ocean interior. This process is called the biological carbon pump. The Southern Ocean is anaemic: Carbon storage in the Southern Ocean currently operates below full capacity because Southern Ocean waters lack a key nutrient, iron, which facilitates plant growth. It has long been thought that iron is predominantly supplied to the Southern Ocean through two main pathways: wind-blown dusts from the continents and resuspension of sediments at the coast. This research was conducted as part of International Polar Year GEOTRACES program, an international collaboration involving Australian (ACE CRC, Hobart) and French (Paris and Brest) scientists.

Authorised by the CEO of the Antarctic Climate and Ecosystems Cooperative Research Centre October 2019.

The ACE CRC was established and supported under the Australian Government’s Cooperative Research Centres Program.

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