Echinoderms contribute to global carbon sink

January 8, 2010
Echinoderms such as brittle stars bury significant amounts of carbon at the seabed when they die and decay. Credit: SERPENT

The impact on levels of carbon dioxide in the Earth's atmosphere by the decaying remains of a group of marine creatures that includes starfish and sea urchin has been significantly underestimated.

" must take this carbon sink into account," says Mario Lebrato, lead author of the study. The work was done when he was at the National Oceanography Centre, Southampton (NOCS) and affiliated with the University of Southampton's School of Ocean and Earth Science (SOES); he is now at the Leibniz Institute of Marine Science in Germany.

Globally, the seabed habitats occupy more than 300 million million square metres, from the intertidal flats and pools to the mightiest deep-sea trenches at 11,000 meters. The benthos - the animals living on and in the sediments - populate this vast ecosystem.

Calcifying organisms incorporate carbon directly from the seawater into their skeletons in the form of inorganic minerals such as calcium carbonate. This means that their bodies contain a substantial amount of inorganic carbon. When they die and sink, some of the inorganic carbon is remineralised, and much of it becomes buried in sediments, where it remains locked up indefinitely.

Lebrato and his colleagues provide the first estimation of the contributions of starfish, , brittle stars, sea cucumbers and sea lilies - all kinds of echinoderm - to the calcium carbonate budget at the seabed. They estimate that the global production from all echinoderms is over a tenth (0.1) of a gigatonne of carbon per year - that is, more than a hundred thousand million kilograms.

This is less than the total biological production in the main water column, or pelagic zone, which scientists believe to be between around 0.6 and 1.8 gigatonnes of carbon per year. But echinoderms apparently deliver more carbon to the sediments than do forams, for example. These microscopic animals live in vast numbers in the oceans and are traditionally regarded along with coccolithophores (single-celled marine plants surrounded by calcium carbonate plates) as one of the biggest contributors to the flux of calcium carbonate from the sunlit surface waters to the ocean's interior - the so-called 'biological carbon pump'.

"Our research highlights the poor understanding of large-scale carbon processes associated with calcifying animals such as echinoderms and tackles some of the uncertainties in the oceanic calcium carbonate budget," says Lebrato: "The realisation that these creatures represent such a significant part of the ocean carbon sink needs to be taken into account in computer models of the biological pump and its effect on global climate."

There is a worry that ocean acidification due to increased carbon dioxide emissions from the burning of fossil fuels could reduce the amount of calcium carbonate incorporated into the skeletons of echinoderms and other calcifying organisms.

However, different echinoderm species respond to ocean acidification in different ways, and the effects of rising temperatures can be as significant as those of rising carbon dioxide. How this will affect the global carbon sink remains to be established.

Lebrato concludes: "The scientific community needs to reconsider the role of benthic processes in the marine cycle. This is a crucial but understudied compartment of the global marine carbon cycle, which has been of key importance throughout Earth history and it is still at present."

Explore further: Fish guts explain marine carbon cycle mystery

More information: Lebrato, M., et al. Global contribution of echinoderms to the marine carbon cycle: a reassessment of the oceanic CaCO3 budget and the benthic compartments. Ecological Monograghs, doi:10.1890/09-0553

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2.3 / 5 (3) Jan 08, 2010
Great article and I'm very happy to see someone is finally looking into the various carbon sinks that have been so greatly underestimated.

4.2 / 5 (5) Jan 08, 2010
Surely you jest. It probably true that carbon sinks have been underestimated or overestimated, or that there are unrecognized carbon sinks, but to suggest that people have not been energetically investigating them suggests a woeful ignorance of the literature. In fact scientists are looking at all sorts of things that effect climate, cloud formation, the role of water vapor, methane and other types of heat trapping gases to refine their models. The error bars right now are quite large and until we understand and integrate all of the major processes affecting climate, the models cannot tell us much more than trends. Scientists KNOW this and also understand that there are large gaps in their knowledge.

One of the ways they know this is because the current models predict a lot less warming than we can actually measure. In addition, the economic and human costs of inaccuracy continue to blossom.
1.6 / 5 (5) Jan 08, 2010
Parsec, I fully agree. However, it's stately clearly above that most carbon sinks of this nature are not often explored. In my opinion that would be because information contrary to the pre-climategate AGW research environment was frowned upon when funding time came around.
3.7 / 5 (3) Jan 09, 2010
In my opinion its because these types of carbon sinks have been considered a) unimportant, and b) difficult to explore. The hidden bias here, and I agree there is one, is that when people pick research projects, they pick those that have the greatest chance of generating positive results.

This is true for ALL types of research, because tenure, reputation, and relative status in the scientific community is biased towards new and/or unexpected results.

Funding is based on studying particular things. Any proposal in any field that suggested they were seeking to determine a given outcome would be rejected out of hand. They seek to confirm positively or negatively a hypothesis, or examine a natural system. The results at the end of the study come after the money has been spent. 95% of all scientists would never change the raw data for any reason. Its a massive breach of professional ethics and is career ending if caught. Peer reviews mean they almost always are.
5 / 5 (4) Jan 09, 2010
People think that peer reviews are just good old boys patting each other on the back. That just isn't so. Most peer reviews are done by people who are professional competitors who delight in finding flaws in others work. I have gone thru this process, and I can tell you it resembles running thru one of those old style gauntlets where everyone has a club and they are trying to beat the crap out of you.

Thats the reason I find most (not all), of the AGW deniers criticism's so irritating. They simply do not have ANY idea of how the system works, and do not trust what they do not know. But it works pretty damn good. 95% of the stuff that gets published is solid and reliable, and the 5% that isn't is pretty quickly found and discarded. As a consequence we have built a highly complex technological civilization where most things work exactly as designed.
not rated yet Jan 09, 2010
"This means that their bodies contain a substantial amount of inorganic carbon. When they die and sink, some of the inorganic carbon is remineralised, and much of it becomes buried in sediments, where it remains locked up indefinitely."

Are there no limits on the amount of carbon that can be captured in this process? Will this go on indefinitely with no effect upon any other processes that are going on at the same time?

ps - thank you for that excellent description of the scientific approval process, Parsec.
2.2 / 5 (5) Jan 09, 2010
This is true for ALL types of research, because tenure, reputation, and relative status in the scientific community is biased towards new and/or unexpected results.
I disagree. One need only look at the Bohr-Schroedinger discussions as evidence to that effect. When a recent theory gains critical acclaim, as did Bohr's model of the atom, anyone attempting to prove fault with the theory is typically given the cold shoulder until their hypothesis proves true in an overwhelming amount of instances.

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