Biogenic sources tracer

An alternative to the above described approaches is the radiocarbon method that allows a distinction of contemporary carbon (from biogenic emissions and combustion of biomass) and carbon from combustion of fossil fuels in particulate carbonaceous matter [15, 41,42]. In contrast to fossil fuels where the 14C isotope is completely depleted, CM emitted from WB shows a contemporary radiocarbon level. Radiocarbon measurements are often combined with measurements of complementary source specific tracers (macro-tracer) for additional information of source impacts [14, 43, 44]. 

For this reason Pb has been used as a tracer of the precipitation fate of S04. Turekian et al. (1989) used the S04 / Pb ratio in aerosols and the flux of °Pb measured in bucket collections to determine the SO flux across the Pacific Ocean. Further, they showed that the S04 / Pb in aerosols from regions of high biological productivity was higher than for normal relatively unpolluted air (Table 3) indicating a sulfate source from the oxidation of dimethyl sulfide (DMS). The measured flux of DMS from the oceans at the equator matched the biogenic flux determined from the °Pb calculation (Table 4). (Actually, as we shall see below, this concordance is probably due to an underestimate of sulfate flux and an overestimate of the fraction of DMS oxidized to sulfate.)... 

Recent advances in analytical instrumentation and methodology promise to add many more geochemical proxies to the palaeoceanographer s toolbox. MC-ICP-MS has opened up a number of isotopic systems previously considered intractable, such as zinc (which shows potential as a tracer of nutrient utilization Vance et al. 2006) and germanium, whose isotopic composition has recently been measured in biogenic opal (Rouxel et al. 2006). Meanwhile improvements in gas source mass spectrometry techniques now permit precise measurement of the abundance of C- 0 bonds in biogenic carbonate. C- 0 abundance shows promise as a palaeothermometer which, unlike 8 0, is independent of the stable isotope composition of seawater (Ghosh et al. 2006). 

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