Effect of photosynthetic light dosage on carbon isotope composition in the coral skeleton: Long‐term culture of Porites spp.

Abstract

[1] Whereas the oxygen isotope ratio of the coral skeleton is used for reconstruction of past information on seawater, the carbon isotope ratio is considered a proxy for physiological processes, principally photosynthesis and respiration. However, the fractionation of carbon isotopes in biogenic carbonate such as coral skeleton is still unclear. We conducted a long-term culture experiment of Porites spp. corals at different light dosages (light intensity, 100, 300, or 500 mmol m À2 s À1 ; daily light period, 10 or 12 h) at 25 ± 0.6°C to examine the contribution of photosynthetic activity to skeletal carbon isotope composition. Corals were grown in sand-filtered seawater and not fed; thus, they subsisted from photosynthesis of symbiotic algae. As the daily dose of photosynthetically active radiation increased, the rate of annual extension also increased. Mean isotope compositions shifted; the carbon isotope compositions (d 13 C) became heavier and the oxygen isotope compositions (d 18 O) became lighter at higher radiation dose. Skeletal d 18 O decrease coincided with increasing skeletal growth rate, indicating the influence of so-called kinetic isotope effects. The observed d 13 C increase should be subject to both kinetic and metabolic isotope effects, with the latter reflecting skeletal d 13 C enrichment due to photosynthesis by symbiotic algae. Using a vector approach in the d 13 C-d 18 O plane, we discriminated between kinetic and metabolic isotope effects on d 13 C. The calculated d 13 C changes from metabolic isotope effects were light dose dependent. The d 13 C fractionation curve related to metabolic isotope effects is very similar to the photosynthesis-irradiance curve, indicating the direct contribution of photosynthetic activity to metabolic isotope effects. In contrast, d 13 C fractionation related to kinetic isotope effects gradually increased as the growth rate increased. Our experiment demonstrated that the kinetic and metabolic isotope effects in coral skeleton were successfully differentiated.Citation: Omata, T., A. Suzuki, T. Sato, K. Minoshima, E. Nomaru, A. Murakami, S. Murayama, H. Kawahata, and T. Maruyama (2008), Effect of photosynthetic light dosage on carbon isotope composition in the coral skeleton: Long-term culture of Porites spp.,

Kinetic and metabolic isotope effects in coral skeletal carbon isotopes: A re-evaluation using experimental coral bleaching as a case study

“…Other methods have estimated the relative intensities of metabolic and kinetic isotope effects using a vector approach (Omata et al, 2005(Omata et al, , 2008. Although they were able to separate metabolic and kinetic isotope effects, this approach is also based on McConnaughey's isotope fractionation model (McConnaughey, 1989a,b) and is therefore similar to the Heikoop et al (2000) data correction approach and assumptions.…”

“…Adkins et al, 2003), it is generally widely accepted and has been supported and applied by many studies (e.g. McConnaughey, 1989b;Allison et al, 1996;Cohen and Hart, 1997;Heikoop et al, 2000;Suzuki et al, 2003;Omata et al, 2005Omata et al, , 2008Suzuki et al, 2005). However, the data correction proposed by Heikoop et al (2000) has never been tested using controlled culturing experiments where the extent of both isotope effects is quantified by simultaneous measurement of the physiological variables that cause fractionation (i.e., photosynthesis, respiration, and calcification) and the paired skeletal stable isotopes values.…”

The effect of carbonic anhydrase on the kinetics and equilibrium of the oxygen isotope exchange in the CO2–H2O system: Implications for δ18O vital effects in biogenic carbonates

“…Unless HCO 3 À (and CO 3 2À ) re-equilibrates before calcification, the 18 O-depletion will be recorded in CaCO 3 . This kinetic model is popularly referred to as a leading explanation for the 18 O depletion in coral skeletons observed in situ and from culture experiments (Allison et al, 1996;Felis et al, 2003;Rosenfeld et al, 2003;Maier et al, 2004;Omata et al, 2008).…”

Reconstruction of the East China Sea palaeoenvironment at 16 ka by comparison of fossil and modern Faviidae corals from the Ryukyus, southwestern Japan

“…In the coral skeleton d 13 C is controlled mainly by photosynthetic activity of symbiotic algae, light conditions and the zooplankton on which the coral feeds (Grottoli, 2002;Omata et al, 2008). Therefore, d 13 C is often considered a proxy for the intensity of solar radiation (Fairbanks and Dodge, 1979;Suzuki et al, 2001).…”