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.
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