Rr. Bidigare et al., Iron-stimulated changes in C-13 fractionation and export by equatorial Pacific phytoplankton: Toward a paleogrowth rate proxy, PALEOCEANOG, 14(5), 1999, pp. 589-595
We present delta(13)C values for phytol, an algal biomarker, which document
up to 7 per mil isotopic enrichment during the IronEx II iron fertilizatio
n experiment. We evaluate these data using a laboratory-derived C-13 fracti
onation model and show this variability is largely the result of elevated g
rowth rates. Isotopic enrichment and stimulation of growth rate were accomp
anied by a sevenfold increase in the export of particulate organic carbon a
s estimated from Th-234 activities. This is the first direct evidence that
enhanced productivity following iron enrichment can lead to both increased
export of organic matter and an associated isotopic signal in an algal biom
arker. On the basis of these results, we propose biomarker isotopic data be
used in conjunction with paleo-CO2 records to reconstruct paleogrowth rate
s. This approach provides a means to test for iron-stimulated changes in al
gal growth in sedimentary records.