Carbon isotropic fractionation of naturally occurring alkenone-producing algae as a function of specific growth rate

Abstract

The taxon-specific nature of a1kenones has allowed development of a novel method to estimate the growth rate of the limited number of species of alkenone producing haptophytes via 13C-labeIled incubation (Popp et al., 2006b). Unlike 14C pigment labeling (Reda1je and Laws, 1981; Welschmeyer and Lorenzen, 1984; Goericke and Welschmeyer 1992a; 1992b; 1993a) and dilution methods (Landry and Hassett, 1982), this novel method allows the specific growth rate of these cells to be measured with close taxon-specificity, even amongst varying algal assemblages or in regions and times where alkenone producing haptophytes do not dominate production of 19'hexanoyloxyfucoxanthin, the pigment most closely associated with these cells (Popp et al.,2006a). The purpose of this study was two-fold. First, the l3e-labelled incubation method for determining 11 was applied in the field, in four very different oceanic regimes, to provide in situ growth rates specific to alkenone producing haptophytes such as E. huxleyi under a wide variety of conditions, including a wide range of upper-ocean soluble reactive phosphate concentrations. This effort illuminated the robustness of the method, and allowed identification of methodological pitfalls to be avoided in future field studies requiring quantification of alkenone-producing haptophyte growth rate. Second, this quantified growth rate was used to evaluate, for the first time, the effect of growth rate on carbon isotopic fractionation under natural conditions.