Carbon isotope compositions of terrestrial C3 plants as indicators of (paleo)ecology and (paleo)climate

TLDR

Modern C3 plant δ13C values rise monotonically as mean annual precipitation decreases, a pattern that contrasts with earlier models, and paleontological data suggest a bias toward dry ecosystems though wet ones are also documented. The study uses altitude‑, latitude‑, and atmospheric CO₂‑corrected δ13C data to refine interpretations of mean annual precipitation, paleodiet, and paleoecology in C3‑dominated ecosystems before 7–8 Ma and at higher latitudes more recently. Temperature, altitude, and latitude corrections are smaller than previously estimated; there is no unambiguous C4 signal before 7–8 Ma and no dense forest evidence at 4.4 Ma, and global biomass analyses show C3 δ13C values are typically overestimated by about 2 ‰.

Abstract

A broad compilation of modern carbon isotope compositions in all C3 plant types shows a monotonic increase in δ 13 C with decreasing mean annual precipitation (MAP) that differs from previous models. Corrections for temperature, altitude, or latitude are smaller than previously estimated. As corrected for altitude, latitude, and the δ 13 C of atmospheric CO 2 , these data permit refined interpretation of MAP, paleodiet, and paleoecology of ecosystems dominated by C3 plants, either prior to 7–8 million years ago (Ma), or more recently at mid- to high latitudes. Twenty-nine published paleontological studies suggest preservational or scientific bias toward dry ecosystems, although wet ecosystems are also represented. Unambiguous isotopic evidence for C4 plants is lacking prior to 7–8 Ma, and hominid ecosystems at 4.4 Ma show no isotopic evidence for dense forests. Consideration of global plant biomass indicates that average δ 13 C of C3 plants is commonly overestimated by approximately 2‰.