Sea creatures' shells grow thinner as CO2 levels rise

Details of the findings are published today (2 August 2002) in Science, by Stephen Barker and Professor Harry Elderfield of the University of Cambridge's Department of Earth Sciences.

Foraminifera are important since they represent one part of the process by which the oceans naturally remove greenhouse gases from the atmosphere. These animals absorb carbon dioxide from the atmosphere and turn it into organic carbon to build their shells. But, ironically, it appears that as the Earth's climate has warmed up since the last ice age, and the levels of carbon dioxide in the sea have risen - making the water more acidic - these organisms have found it harder to build their shells.

The project is jointly led by Professor Harry Elderfield, and Professor Edward Boyle in the Earth, Atmospheric and Planetary Sciences department at the Massachusetts Institute of Technology (MIT). The research forms part of a CMI study into the science and feasibility of pumping greenhouse gases into the ocean to remove more carbon dioxide from the atmosphere. The issue is of interest to scientists, environmentalists and industry.

Stephen Barker and Harry Elderfield, co-authors of the Science paper, say:

"One proposed approach is to capture the carbon dioxide produced by fossil fuel burning and put it out of harm's way. Some researchers are looking at ways to help the oceans sequester more carbon. For example, could we encourage the growth of plants living at the surface of the sea (which absorb carbon dioxide) by feeding them a nutrient, like iron?

"In order to know if this method would work, we need to understand the very complex processes by which oceans naturally regulate and remove carbon dioxide from the atmosphere. Then we can say to industry and government, 'this is the science of what you propose, and here are the possible options'. In other words, the role of the scientist is to discover what the consequences might be of any particular perturbation of the natural environment."

For this part of the work, the CMI research team studied foraminifera found in sediment cores extracted from the seabed in the North Atlantic, just south of Iceland. Some of the sediment dates back 20,000 years when carbon dioxide levels in the atmosphere and in sea water were lower than they are now.

Stephen Barker, a graduate student, measured the composition of the shells of those foraminifera, and compared them to those found in much more recent sediment cores, dating from around the pre-industrial era of 1800.

"The change he saw was striking. The shells of the foraminifera are half the weight in recent times that they were in glacial times. Our findings tie in with the findings of research teams that have studied other calcifying - or shell-creating - organisms like corals, and a group of sea plants known as coccolithophores," says Professor Elderfield.

He adds:

Professor Boyle says:

"Although chemical oceanographers have realized its importance for many years, it has been very difficult to make quantitative reconstructions of the past carbonate saturation state of the ocean. Harry is creating a new approach to this difficult problem that will inject fresh understanding into this subject.

This new approach dovetails with research that I and Jonathan Erez (of Hebrew University) are conducting on the use of sulfate in foraminifera as a carbonate ion indicator, and I am pleased that CMI is giving us the chance to work together to pursue these new approaches."

Prof Ekhard Salje, Cambridge Director of CMI's integrated research programme, believes the project is of major importance.

"To reduce the level of emissions of greenhouses gases will become one of the main research goals of this decade. In order to proceed with this research we need to assess how marine life has been influenced by CO2 emission in the geological past, and we need then to analyse if CO2 sequestration in the ocean is ecologically acceptable. The results by Elderfield and Barker represent a first milestone in this research because they allow the first quantitative assessment of the effect of CO2 and temperature on marine life."