Structure of the carbon isotope excursion in a high-resolution lacustrine Paleocene-Eocene Thermal Maximum record from central China

- The first complete lacustrine PETM section has been recovered from central China.
- The true magnitude of the carbon isotope excursion is likely close to −4‰.
- Multisubstrate δ13C presents a gradual carbon isotope excursion onset.
- The PETM was not a single, decadal-scale carbon release event.
- 13C-depleted carbon release operated as a positive feedback to temperature rise.

The carbon isotope excursion (CIE) associated with the Paleocene-Eocene Thermal Maximum (PETM) has been recognized for the first time in the micritic carbonate, total organic carbon (TOC) and black carbon (BC) contained within the lacustrine sediments from the Nanyang Basin, central China. The remarkably large excursion (∼−6‰) in the δ13CTOC and δ13CBC values is possibly attributable to increased humidity and elevated pCO2 concentration. The ∼−4‰ CIE recorded in the δ13Ccalcite, reflecting the average isotope change of the watershed system, is consistent with that observed in planktonic foraminifera. This correspondence suggests that the true magnitude of the carbon isotope excursion in the ocean-atmosphere system is likely close to −4‰. The ∼10 m excursion onset in our multi-proxy δ13C records demonstrates that the large input of 13C-depleted carbon into the ocean-atmosphere system was not geologically instantaneous. Despite difference and somewhat smoothness in detailed pattern of the CIE due to localized controls on different substrates, inorganic and organic δ13C data generally depict a gradual excursion onset at least over timescales of thousands of years. In addition, continental temperature reconstruction, based on the distribution of membrane lipids of bacteria, suggests a warming of ∼4 °C prior to the PETM and ∼7 °C increase in temperature during the PETM. The temperature data are overall similar in pattern and trend to the δ13C change across the PETM. These observations, combined with pre-CIE warming, are in line with the idea that 13C-depleted carbon release operated as a positive feedback to temperature, suggesting supply from one or more large organic carbon reservoirs on Earth's surface.