Eos, Transactions American Geophysical Union

Examining nitrogen isotope ratios as a paleoproxy



The relative consumption of nutrients by diatoms in the ocean, with regard to both supply and demand of nitrate, affects the nitrogen isotope composition of diatoms. Sedimentary nitrogen isotope ratios are often used as a proxy for past conditions. However, there are uncertainties associated with these nitrogen isotope proxies. Bulk sediment nitrogen isotope ratios differ from fossil diatom-bound nitrogen isotope ratios. To learn more about these uncertainties, Horn et al. measured nitrogen isotopes in five different species of cultured diatoms. The results indicate that there are significant interspecies variations in the offsets between isotope ratios in the total biomass and isotope ratios in the diatom-bound nitrogen. These differences should be considered when interpreting nitrogen isotope ratios. (Paleoceanography, doi:10.1029/2010PA002080, 2011)