An experimental study of carbon-isotope fractionation between diet, hair, and feces of mammalian herbivores

The carbon-isotope composition of hair and feces offers a glimpse into the diets of mammalian herbivores. It is particularly useful for determining the relative consumption of browse and graze in tropical environments, as these foods have strongly divergent carbon-isotope compositions. Fecal δ13C values reflect the last few days consumption, whereas hair provides longer term dietary information. Previous studies have shown, however, that some fractionation occurs between dietary δ13C values and those of hair and feces. Accurate dietary reconstruction requires an understanding of these fractionations, but few controlled-feeding studies have been undertaken to investigate these fractionations in any mammalian taxa, fewer still in large mammalian herbivores. Here, we present data from the first study of carbon-isotope fractionation between diet, hair, and feces in multiple herbivore taxa. All taxa were fed pure alfalfa (Medicago sativa) diets for a minimum period of 6 months, at which point recently grown hair was shaved and analyzed for carbon isotopes. The mean observed diethair fractionation was +3.2, with a range of +2.7 to +3.5. We also examined dietfeces fractionation for herbivores on alfalfa and bermudagrass (Cynodon dactylon) feeds. The mean dietfeces fractionation for both diets was 0.8, with less fractionation for alfalfa (0.6) than bermudagrass (1.0). Fecal carbon turnover also varies greatly between taxa. When diets were switched, horse (Equus caballus) feces reflected the new diet within 60 h, but alpaca (Lama pacos) feces did not equilibrate with the new diet for nearly 200 h. Thus, fecal carbon isotopes provide far greater dietary resolution for hindgut-fermenting horses than foregut-fermenting alpacas.

Download Full-text

The Carbon-Isotope Record of the Sub-Seafloor Biosphere

Geosciences ◽

10.3390/geosciences9120507 ◽

2019 ◽

Vol 9 (12) ◽

pp. 507 ◽

Cited By ~ 3

Author(s):

Patrick Meister ◽

Carolina Reyes

Keyword(s):

Carbon Isotope ◽

Carbon Isotopes ◽

Isotope Fractionation ◽

Dissolved Inorganic Carbon ◽

Isotopic Signature ◽

Enzymatic Reactions ◽

Deep Biosphere ◽

Geological Time ◽

Isotopic Signatures ◽

Carbon Isotope Fractionation

Sub-seafloor microbial environments exhibit large carbon-isotope fractionation effects as a result of microbial enzymatic reactions. Isotopically light, dissolved inorganic carbon (DIC) derived from organic carbon is commonly released into the interstitial water due to microbial dissimilatory processes prevailing in the sub-surface biosphere. Much stronger carbon-isotope fractionation occurs, however, during methanogenesis, whereby methane is depleted in 13C and, by mass balance, DIC is enriched in 13C, such that isotopic distributions are predominantly influenced by microbial metabolisms involving methane. Methane metabolisms are essentially mediated through a single enzymatic pathway in both Archaea and Bacteria, the Wood–Ljungdahl (WL) pathway, but it remains unclear where in the pathway carbon-isotope fractionation occurs. While it is generally assumed that fractionation arises from kinetic effects of enzymatic reactions, it has recently been suggested that partial carbon-isotope equilibration occurs within the pathway of anaerobic methane oxidation. Equilibrium fractionation might also occur during methanogenesis, as the isotopic difference between DIC and methane is commonly on the order of 75‰, which is near the thermodynamic equilibrium. The isotopic signature in DIC and methane highly varies in marine porewaters, reflecting the distribution of different microbial metabolisms contributing to DIC. If carbon isotopes are preserved in diagenetic carbonates, they may provide a powerful biosignature for the conditions in the deep biosphere, specifically in proximity to the sulphate–methane transition zone. Large variations in isotopic signatures in diagenetic archives have been found that document dramatic changes in sub-seafloor biosphere activity over geological time scales. We present a brief overview on carbon isotopes, including microbial fractionation mechanisms, transport effects, preservation in diagenetic carbonate archives, and their implications for the past sub-seafloor biosphere and its role in the global carbon cycle. We discuss open questions and future potentials of carbon isotopes as archives to trace the deep biosphere through time.

Download Full-text

Fractionation of Carbon Isotopes Between C-O-H Fluids and Melts in High Temperature Systems - Experimental Developments and Outlook

10.5194/egusphere-egu2020-21481 ◽

2020 ◽

Author(s):

Paul Petschnig ◽

Nico Kueter ◽

Max Schmidt

Keyword(s):

High Temperature ◽

Carbon Isotope ◽

Isotope Fractionation ◽

Isotope Composition ◽

Stable Carbon Isotope ◽

Experimental Studies ◽

Magma Ocean ◽

Carbon Isotope Fractionation ◽

The Earth ◽

Carbon Compounds

Whether in gases or fluids, as solid or liquid carbonates, dissolved in magma or precipitated in its elemental form, carbon is present in every domain on Earth. The pathways of carbon across atmospheric-, surface-, subduction- and deeper reservoirs of our planet are complex, but can be illuminated by tracing stable carbon isotope ratios. Carbonates take a key role in connecting the surface to the deep carbon cycle. At moderate temperatures, carbon compounds dissolve in fluids, above 1000 &#176;C, carbonates dissolve in or form melts and mobilize carbon inside the Earth. Towards the crust, carbon compounds tend to be oxidized (e.g. CO2, CO32-) while in the deeper mantle (> 6-8 GPa), reduced states are dominant and cause carbonate reduction to CH4, FeC or C dissolved in metal, graphite or diamond.[1]Recent experimental studies show large carbon isotope fractions at temperatures relevant for the mantle and early Earth environments (i.e. magma ocean surfaces). High temperature equilibrium fractionations have been constrained for CH4-CO2-CO[2], carbonate - graphite[3], and FeC - graphite[4]&#160;systems, most pairs amounting to a few &#8240; at 1000 oC. The recognition of kinetic carbon isotope fractionation during elemental carbon precipitation from C-O-H fluids revealed an unexpected high-temperature fractionation mechanism of ~5 &#8240; for lower crust and mantle temperatures[5]. In this light, carbon isotope fractionation may yield surprises in other experimentally underexplored processes.&#160;We present internally consistent experimental data on high temperature carbon isotope fractionation between carbonate or silicate melts, carbonate, C-O-H-fluids, carbide and graphite. Our results suggest that at high temperatures (>1000 &#176;C) the bonding environment of CO3-groups (i.e. either in depolymerized silicate- or carbonate melt, in which carbon is anionic CO32-, or as calcite) causes no resolvable differences leading to a universal &#8710;13C (CO2 -CO32-) fractionation function. Similarly, we suggest that granitic melts with all carbon as molecular CO2will show no isotope fractionation with an oxidized high temperature fluid. We further discuss challenges of experimental setups under reducing fO2conditions and the intent of equilibrating silicate melt with reduced C-O-H-fluids, which is experimentally unconstrained and required to understand on one hand the magmatic outgassing of the Earth and how to reconstruct the source isotope composition, on the other hand in a magma-ocean setting, where reduced species are key for the evolution of primitive carbon reservoirs and their isotopic ratios (i.e. mantle carbon).&#160;[1] Rohrbach, A., Schmidt, M. (2011).&#160;Nature&#160;472,&#160;209&#8211;212.[2] Kueter, N., Schmidt, M. W., Lilley M. D., Bernasconi, S.M. (2019b). EPSL 506, p.64-75. [3] Kueter, N., Lilley, M.D., Schmidt, M.W., Bernasconi, S.M. (2019a). GCA253, 290&#8211;306. [4] Satish-Kumar, M., So, H., Yoshino, T., Kato, M., Hiroi, Y. (2011). EPLS 310, 340&#8211;348. [5]Kueter, N., Schmidt, M. W., Lilley M. D., Bernasconi, S.M. (2020). EPSL 529,115848&#160;

Download Full-text

Carbon isotope fractionation by photosynthetic aquatic microorganisms: experiments with Synechococcus PCC7942, and a simple carbon flux model

Canadian Journal of Botany ◽

10.1139/b98-067 ◽

1998 ◽

Vol 76 (6) ◽

pp. 1109-1118 ◽

Cited By ~ 3

Author(s):

Jonathan Erez ◽

Anne Bouevitch ◽

Aaron Kaplan

Keyword(s):

Carbon Isotope ◽

Carbon Isotopes ◽

Isotope Fractionation ◽

Isotopic Fractionation ◽

Bisphosphate Carboxylase ◽

Carbon Isotope Fractionation ◽

Concentrating Mechanism ◽

Aquatic Microorganisms ◽

Synechococcus Pcc7942 ◽

Flux Model

Stable carbon isotopes (12C and 13C) are widely used to trace biogeochemical processes in the global carbon cycle. Natural fractionation of carbon isotopes is mainly due to the discrimination of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) against 13C during photosynthesis. In marine and other aquatic microorganisms, this fractionation is lowered when the dissolved CO2 (CO2(aq)) is decreasing, but the underlying mechanisms are poorly understood. Cultured Synechococcus PCC7942 showed maximum isotopic fractionations of -33omicron (in delta 13C units) relative to the total inorganic carbon (Ci) when CO2(aq) is above 30 m M. As the culture grew, pH increased, CO2(aq) was lower than 1 m M, and the Ci concentrating mechanism was induced although the Ci was above 3 mM. The isotopic fractionation was drastically reduced to values of -1 to -3 omicron relative to Ci. A simple carbon isotope flux model suggests that during the first stages of the experiment the total uptake (F1) was roughly three- to four-fold greater than the photosynthetic net accumulation (F2). When the Ci concentrating mechanism was induced, the leakage of CO2 from the cells declined, the cells started to utilize HCO3- and the F1/F2 ratio decreased to values close to 1. Based on this model the isotopic variability of oceanic phytoplankton suggests that the F1/F2 ratio may be above 3 in high latitudes and ~1.1 in equatorial waters, where the Ci concentrating mechanism is probably induced. Attempts to reconstruct past atmospheric CO2 levels and paleoproductivity should take into account the effects of the Ci concentrating mechanism on the isotopic fractionation of aquatic primary producers.Key words: carbon concentrating mechanism, carbon isotope fractionation, CO2, photosynthesis.

Download Full-text

Carbon isotope fractionation in various forms of biogenic organic matter: I. Partitioning of carbon isotopes between the main polymers of higher plant biomass

Geochemistry International ◽

10.1134/s0016702910120013 ◽

2010 ◽

Vol 48 (12) ◽

pp. 1157-1165 ◽

Cited By ~ 11

Author(s):

L. A. Kodina

Keyword(s):

Organic Matter ◽

Carbon Isotope ◽

Carbon Isotopes ◽

Isotope Fractionation ◽

Plant Biomass ◽

Higher Plant ◽

Carbon Isotope Fractionation

Download Full-text

VOLCANISM DRIVEN CARBON ISOTOPE FRACTIONATION ACROSS THE WUCHIAPINGIAN-CHANGHSINGIAN BOUNDARY INTERVAL: IMPLICATIONS FROM 187OS/188OS ISOTOPE STRATIGRAPHY

10.1130/abs/2018am-316949 ◽

2018 ◽

Author(s):

Zeyang Liu ◽

◽

David Selby ◽

Hua Zhang ◽

Quanfeng Zheng ◽

...

Keyword(s):

Carbon Isotope ◽

Isotope Fractionation ◽

Carbon Isotope Fractionation ◽

Isotope Stratigraphy

Download Full-text

Carbon Isotope Fractionation during the Formation of CO2 Hydrate and Equilibrium Pressures of 12CO2 and 13CO2 Hydrates

Molecules ◽

10.3390/molecules26144215 ◽

2021 ◽

Vol 26 (14) ◽

pp. 4215

Author(s):

Hiromi Kimura ◽

Go Fuseya ◽

Satoshi Takeya ◽

Akihiro Hachikubo

Keyword(s):

Carbon Isotope ◽

Isotope Fractionation ◽

Small Difference ◽

Hydrate Formation ◽

Formation Temperature ◽

Carbon Isotope Fractionation ◽

Unit Cell Size ◽

Naturally Occurring ◽

Three Phase ◽

The Difference

Knowledge of carbon isotope fractionation is needed in order to discuss the formation and dissociation of naturally occurring CO2 hydrates. We investigated carbon isotope fractionation during CO2 hydrate formation and measured the three-phase equilibria of 12CO2–H2O and 13CO2–H2O systems. From a crystal structure viewpoint, the difference in the Raman spectra of hydrate-bound 12CO2 and 13CO2 was revealed, although their unit cell size was similar. The δ13C of hydrate-bound CO2 was lower than that of the residual CO2 (1.0–1.5‰) in a formation temperature ranging between 226 K and 278 K. The results show that the small difference between equilibrium pressures of ~0.01 MPa in 12CO2 and 13CO2 hydrates causes carbon isotope fractionation of ~1‰. However, the difference between equilibrium pressures in the 12CO2–H2O and 13CO2–H2O systems was smaller than the standard uncertainties of measurement; more accurate pressure measurement is required for quantitative discussion.

Download Full-text