CO2aq-dependent photosynthetic 13C fractionation in the ocean: A model versus observations

A theoretical model of CO2aq-dependent phytoplankton carbon isotope fractionation (єp) and abundance (δ13Corg) is compared to observed isotopic trends with temperature and [CO2aq] in the ocean. It is shown that the model's δ13Corg response to surface ocean temperature and to [CO2aq] can simulate observed trends when the other independent model variables (phytoplankton cell growth rate, cell size, cell membrane CO2 permeability, and enzymatic isotope fractionation) are held at realistic, constant values. The possible contribution made by each of these variables to the residual scatter in δ13Corg about its trends with temperature and [CO2aq] is quantified, thus estimating a maximum isotopic sensitivity to changes in each of these variables. The model response to growth rate and especially cell size, however, appears to be unrealistically high. This may occur because the net isotopic effects of such factors may be attenuated through dependent and isotopically offsetting variations among variables. The model's indicated sensitivity to such factors as CO2 permeability, enzymatic fractionation, cell size, and cell surface area/volume provides mechanisms whereby changes in species composition can play a significant role in affecting observed variations in oceanic δ13Corg. Overall, the model is consistent with earlier suggestions that marine δ13Corg and єp variability can be explained by carbon isotope fractionation evoked by CO2aq-dependent phytoplankton. This has important implications for interpreting carbon isotopic variability encountered in plankton and their organic constituents in the present-day ocean and in the marine sedimentary record

Variance in isotopic signatures as a descriptor of tissue turnover and degree of omnivory

1. Diet analyses using C and N stable isotopes commonly focus on mean isotopic signatures; however, isotopic variance among individuals is likely to also contain useful information including details of omnivory. 2. Changes in isotopic signature as a result of dietary shifts are not instantly manifest in the isotopic signature of consumer tissues, but lagged over a period of time required for equilibration. Tissue turnover times have not previously been described in terms of variance in isotopic signature among individuals, and variance among individuals following equilibration with a constant diet is limited. 3. Temporal changes in d15N and d13C variance in juvenile European Sea Bass (Dicentrarchus labrax) muscle, heart and liver were monitored following a shift from a wild diet to two single-source diets administered under seminatural conditions in captivity. Exponential decay functions of the standard deviation of d15N and d13C among individuals were used to model changes in variance over time. 4. All tissues exhibited a similar rate of tissue turnover using variance. However, variance among individuals within tissue types differed once fishes were equilibrated with the laboratory diet. The coefficients of variation of d13C and d15N were smallest in muscle and greatest in liver and greater among sampling dates than within. 5. Analysis of d15N and d13C in different tissues will not therefore provide equivalent power to detect differences in diet or to track changes in patterns of omnivory. Analysis of omnivory should be restricted to variance from a single tissue type. Of the tissues considered here, white muscle is most appropriate for this purpose. 6. Variance estimates derived here provide minimum values expected for a highly specialist feeding population. Departure from these values can be used to describe the degree of omnivory within a population

Erratum: Farming with crops and rocks to address global climate, food and soil security (Nature Plants (2018), DOI: 10.1038/s41477-018-0108-y)

In the version of this Perspective originally published, 'acidification' was incorrectly spelt as 'adification' in Fig. 4. This has now been corrected. © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved

ELECTRON-IMPACT IONIZATION OF ATOMIC-HYDROGEN

JETZKE S, ZAREMBA J, Faisal F. ELECTRON-IMPACT IONIZATION OF ATOMIC-HYDROGEN. ZEITSCHRIFT FUR PHYSIK D-ATOMS MOLECULES AND CLUSTERS. 1989;11(1):63-69