Increased Stability in Carbon Isotope Records Reflects Emerging Complexity of the Biosphere

Abstract

Preference for certain stable isotopes (isotope fractionation) during enzyme-mediated reactions is a universal aspect of life. For instance, carbon isotopes are fractionated during anabolic (e.g., photosynthate production) and catabolic (e.g., methanogenesis) reactions. These biological processes exert a major control on ambient micro-scale chemical conditions as well as the large-scale exogenic carbon reservoir. Combined with the ubiquity of bio-mediated carbonate mineral nucleation and obligate enzymatic skeletonization, these biochemical reactions and their control on the exogenic carbon pool are known to leave distinct imprints on carbonate minerals which accumulate as sediments throughout Earth's history. Here, we study the evolution of the marine carbonate-carbon isotope record based on database compilations from the Precambrian and the Phanerozoic. By looking at the frequency distribution of the amplitude of stratigraphic variation at various temporal resolutions, we assess trends in the carbonate-carbon isotope variability. Part of this variation can only be explained by authigenic and diagenetic carbonate mineral additions, which carry metabolic carbon isotope signatures created in the vicinity of cells and secluded (sub-)seafloor micro-environments. It can be envisioned that compartmentalization (membrane enclosed regions), the accumulation of extracellular polymeric substances (biofilms), and restricted fluid exchange in the early diagenetic environment can create sharp isotope gradients that lead to a high-order of micro-scale carbon isotope variability being imprinted in carbonate rock. The frequency of the high-amplitude variation diminishes with the development of more complex life (metazoan-dominated biosphere); presumably through the dispersing action of bioturbation (eradicating these micro-environments), increased grazing pressure and the advent of obligate biomineralization. On the other hand, stark chemical gradients in a world dominated by unicellular life (prokaryotes and to a lesser extent eukaryotes) are thought to leave a distinctly more variable C isotope signature in carbonate rock. An enhanced understanding of the biogenicity of carbonate carbon isotope signatures at multiple spatial and temporal scales provides a baseline that is usable in the search for signs of (past) extraterrestrial life.

Selection by differential survival among marine animals in the Phanerozoic

“…If, as Doolittle [5] suggests, the cumulative effect of SDS on a planetary scale may have been a self-stabilizing biosphere , it is also natural to ask if animals themselves may have any substantive part to play in it. In many ways, animal activity does contribute to homeostasis of the environment [27]: marine calcifiers make their skeletons out of carbonate which partakes in the buffer system enhancing the ocean’s carbon dioxide uptake [28], bioturbation stabilizes the carbon cycle by mixing the sea floor [29], and heterotrophy by zooplankton acts as a control on algal blooms [30]. This is not to say that animals are responsible for any possible Gaian properties of the system (which would have been established billions of years before their emergence), but that, like all lineages, even animals can contribute to overall stability.…”

Depthwise microbiome and isotopic profiling of a moderately saline microbial mat in a solar saltern

“…In GN microbial mats, for example, variability in the δ 13 C org signatures were indicative of alternating dominance by phototrophs, whereas the bulk signature was shown to be overprinted by the heterotrophic activities of sulfate-reducers and methanogens 97 . In addition, physicochemical conditions and any post-sedimentation modifications are discounted in interpreting the values 98 , 99 .…”

The use of lntramolecular carbon isotope distributions (13c/12c) of biomolecules to study temporal organization of post-photosynthetic metabolism in a plant cell

“…DOI: https://dx.doi.org/10.17352/ab.000006 and physiological tasks, which arise when it is necessary to investigate the metabolism of an unexplored organism or to identify the pathway of synthesis of an unknown compound [5,6]. The applications of the 13 C distribution technique to various geochemical tasks, including distinguishing biogenic or abiogenic life [7] the investigations of organic compounds associated with extraterrestrial life or with life in extreme conditions and other studies in related fi elds of knowledge [8,9]. Below we will consider a method for determining the spatial and temporal organization of metabolism in organisms based on the analysis of the relationship between the metabolic pathway and carbon isotope distribution in biomolecules.…”