Palaeoclimate and palaeoecology at the end of the Late Palaeozoic Ice Age: Insights from the Lower Permian Bioarchive of Oman

The late Sakmarian (Early Permian) is a key time-interval to unravel deep time climate changes at the transition from icehouse to greenhouse conditions. Very recent data (Jurikova et al., 2025) showed that the demise of the Late Palaeozoic Ice Age (LPIA) was caused by an increase in atmospheric CO₂ linked to volcanic activity, peaking in the late Sakmarian. To understand how this CO₂ increase impacted the climate at the seasonal scale and how it affected marine ecosystems, we performed a sclerochemical analysis on a carefully screened shell of the brachiopod Pachycyrtella omanensis from the Saiwan Fm. in Oman. This specimen thrived at ~45°S, in shallow water settings along the Gondwanan margin, in the context of the deglaciation from the LPIA and Early Permian warming.

High-resolution δ¹⁸O, δ¹³C and δ¹¹B sclerochemical analyses along the shell growth axis revealed oscillating profiles, characterized by at least three main periodic cycles each. Preliminary profile analysis points towards broad coupling of main internal δ¹³C and δ¹¹B cycles, showing a maximum signal amplitude of ~3‰ and 5‰, respectively, which might be representative of growth cycles punctuated with growth halts in between.

Periodicity in the δ¹⁸O profile showed a maximum signal amplitude of 3.2‰ and might correspond to seasonal variations in seawater temperature. Based on the average δ¹⁸O and signal amplitude, and assuming a δ¹⁸O_sw value of –0.5‰, this specimen recorded an average temperature of 25.5°C with a temperature seasonality of 15°C. The average temperature recorded by P. omanensis is much higher than what is observed at similar latitudes and depths nowadays, as is the seasonal variation. The relatively higher average temperature could be explained by the warming and increasing CO₂ conditions during the Early Permian. Elevated seasonality is not expected under these conditions, but it may have been magnified by seasonally variable δ¹⁸O_sw reflecting a dynamic coastal environment, which could also explain the observed internal cyclicity in δ¹³C and δ¹¹B.

This study underlines the potential of sclerochemical analyses in well-preserved fossil brachiopods for providing news insights into deep-time environmental change at annual/ seasonal scale. Our results also lend support to the hypothesis that P. omanensis might have been an opportunistic species that exploited dynamic environments subjected to seasonal stressors with oscillating but abundant food resources. These findings suggest a potential analogue scenario for future marine ecosystems under the current warming icehouse.

 

Jurikova H., Garbelli C., Whiteford R., Reeves T., Laker G., Liebetrau V., Gutjahr M., Eisenhauer A., Savickaite K., Leng M.J., Iurino D.A., Viaretti M., Tomašových A., Zhang Y., Wang W., Shi G.R., Shen S.Z., Rae J.W.B. & Angiolini L. (2025). Rapid rise in atmospheric CO₂ ended the Late Palaeozoic Ice Age. Nature Geoscience.