CARBON EXPORT

New approaches for understanding oceanic carbon uptake

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 Obiettivo del progetto (Objective)

'The oceans play a crucial role in the uptake of atmospheric carbon dioxide (CO2), a man-made greenhouse gas that strongly influences global climate. Certain marine organisms are hypothesized to greatly enhance CO2 removal during growth. A percentage of these cells subsequently sink, transporting the C to depth where it remains for millennia. Research has shown that one such group of organisms, di-nitrogen (N2) fixers or diazatrophs, are much more globally prevalent than previously thought and may even be further enhanced near zones of intense subsurface denitrification. As such, we propose to examine how the interactions between denitrification and N2 fixation contribute to particle export in one such area, the Gulf of California and adjacent waters of the eastern tropical North Pacific. Measuring what controls the magnitude, timing, and depth of particle export in marine systems is difficult. Here, we will use the short-lived radioisotope pairs 234Th:238U and 210Po:210Pb to measure diazatroph mediated particle formation, export, and remineralization in samples to be collected during a funded cruise (U.S. NSF) in the N. Pacific in August 2008. Preliminary studies suggest that when used in tandem, these radionuclide pairs provide unique temporal and spatial insight into the mechanisms that modulate marine biotic and abiotic particle formation and sinking throughout the water column. This proposal combines the expertise of two renowned radiochemists and will allow for an international exchange of cutting edge analytical techniques. Results will include much needed improvements in radiochemical export models that can be applied in a range of ecosystems. Understanding what controls particle formation and export in marine systems will provide insight into what may control regional and global climate as well as the transport and fate of other particle reactive pollutants such as heavy metals and organic contaminants.'

Introduzione (Teaser)

In an effort to improve our understanding of carbon uptake by the oceans, a research team travelled to the Gulf of California to study a special group of micro-organisms.

Descrizione progetto (Article)

While it is well known that the oceans are a major sink for carbon from the atmosphere, the exact mechanisms through which this export takes place are not well understood. It has been suggested that nitrogen-fixing organisms, known as diazotrophs, have an important role to play here.

EU funding was set aside to examine this aspect in detail through the 'New approaches for understanding oceanic carbon uptake' (Carbon Export) project. In this context, a well-equipped research vessel was deployed to the Gulf of California to perform extensive sampling of its biologically rich waters.

Measurements of nitrogen fixation at several depths have indicated a strong dependence both on the type of organisms present in the plankton mix and on sea-surface temperature. Evidence of a substantial contribution to carbon fixation made by unicellular Group A diazotrophs was found in colder waters just outside the Gulf.

In addition, two naturally occurring radioisotopes, 234Th and 210Po, have been used to measure the carbon flux from the sea surface downwards. As expected, carbon export was very high in regions where the plankton population was enriched with diatoms. However, large fluxes were also recorded in areas with unicellular Group A diazotrophs. In fact, analysis revealed that they were much more efficient than diatoms at exporting carbon.

These findings will allow for more accurate carbon cycling in global models and consequently help improve their predictions of future climate change.