Burkhardt, S. Alfred Wegener Institute for Polar and Marine Research, sburkhardt@awi-bremerhaven.de
Riebesell, U. Alfred Wegener Institute for Polar and Marine Research, uriebesell@awi-bremerhaven.de
Zondervan, I. Alfred Wegener Institute for Polar and Marine Research, izondervan@awi-bremerhaven.de

 
SPECIES-SPECIFIC RESPONSE OF STABLE CARBON ISOTOPE FRACTIONATION BY MARINE PHYTOPLANKTON TO VARIATION IN DAYLENGTH, GROWTH RATE, AND CO2 AVAILABILITY
 
Recent evidence from laboratory experiments revealed an inverse correlation between stable carbon isotope fractionation and the ratio of growth rate and CO2 concentration, [CO2], in eukaryotic marine phytoplankton (e.g. Popp et al. 1998). This raises the possibility of estimating in situ growth rates of phytoplankton or ancient [CO2] from sedimentary isotope data. In these studies, growth rates were controlled by nitrogen supply. Here, we induced changes in instantaneous growth rate (rate of C assimilation during the photoperiod) of 7 marine phytoplankton species by variation of daylength at different [CO2]. In 4 of the species tested, isotope fractionation was 4-6 per mill lower in a 16h:8h L/D cycle than under continuous light. In these species, the effect of growth rate on fractionation was larger than the effect of [CO2], which caused less than 3 per mill variability. The remaining species tested showed a similar dependence on [CO2] but were insensitive to daylength-related differences in instantaneous growth rate. This group includes Phaeodactylum tricornutum, which shows growth-rate dependent fractionation under N-limited conditions. Thus, growth-rate related effects on fractionation apparently depend on the factor controlling growth rate. This suggests that a general relationship between isotope fractionation and growth rate/[CO2] may not exist.
 
Day: Monday, Feb. 1
Time: 03:30 - 03:45pm
Location: Eldorado Hotel
 
Code: SS32MO0330E