Lipid biomarkers record fundamental changes in the microbial community structure of tropical seas during the Late Ordovician Hirnantian glaciation

A significant discovery from the Late Ordovician Hirnantian glaciation reveals that enhanced methane cycling played a crucial role in climate feedback during warm intervals. This was evidenced by high abundances of 3β-methylhopanes, sourced from aerobic methanotrophic bacteria, which were found to correlate positively with paleotemperature proxies across multiple tropical marine basins. The study analyzed lipid biomarkers in thermally preserved strata from Anticosti Island (Canada), the Cincinnati Arch (USA), and Nevada (USA). Despite oceanographic differences, these localities showed similar biomarker profiles, particularly in hopane/sterane ratios, indicating shifts in bacterial versus algal primary production. The findings suggest that methane cycling could have been a key positive feedback mechanism on climate during extended warm periods of early Paleozoic time.

Rohrssen, M., Love, G. D., Fischer, W., Finnegan, S., & Fike, D. A. (2013). Lipid biomarkers record fundamental changes in the microbial community structure of tropical seas during the Late Ordovician Hirnantian glaciation. Geology, 41(2), 127–130. https://doi.org/10.1130/g33671.1