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Title: Carbon Isotope Fractionation in Noelaerhabdaceae Algae in Culture and a Critical Evaluation of the Alkenone Paleobarometer
Abstract

The carbon isotope fractionation in algal organic matter (εp), including the long‐chain alkenones produced by the coccolithophorid family Noelaerhabdaceae, is used to reconstruct past atmospheric CO2levels. The conventional proxy linearly relates εpto changes in cellular carbon demand relative to diffusive CO2supply, with larger εpvalues occurring at lower carbon demand relative to supply (i.e., abundant CO2). However, the response ofGephyrocapsa oceanica, one of the dominant alkenone producers of the last few million years, has not been studied closely. Here, we subjectG. oceanicato various CO2levels by increasing pCO2in the culture headspace, as opposed to increasing dissolved inorganic carbon (DIC) and alkalinity concentrations at constant pH. We note no substantial change in physiology, but observe an increase in εpas carbon demand relative to supply decreases, consistent with DIC manipulations. We compile existing Noelaerhabdaceae εpdata and show that the diffusive model poorly describes the data. A meta‐analysis of individual treatments (unique combinations of lab, strain, and light conditions) shows that the slope of the εpresponse depends on the light conditions and range of carbon demand relative to CO2supply in the treatment, which is incompatible with the diffusive model. We model εpas a multilinear function of key physiological and environmental variables and find that both photoperiod duration and light intensity are critical parameters, in addition to CO2and cell size. While alkenone carbon isotope ratios indeed record CO2information, irradiance and other factors are also necessary to properly describe alkenone εp.

 
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NSF-PAR ID:
10366963
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Geochemistry, Geophysics, Geosystems
Volume:
22
Issue:
7
ISSN:
1525-2027
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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