Early Triassic Cycling of Pyrogenic Carbon in Northern High Latitudes

The Permian-Triassic mass extinction (PTME) is considered to be the most severe extinction in Earth’s history. Following this extinction, the Early Triassic is known as an interval of divergent biotic recovery patterns, with several periods of unfavorable environmental conditions as suggested by global fluctuations in carbon isotope compositions of both organic and inorganic carbon reservoirs (e.g., Payne et al., 2004; Galfetti et al., 2007). Despite these global carbon isotope excursions, little is known about the evolution of the organic carbon cycle. The aim of this study is to improve our understanding of long-term organic carbon cycle dynamics, in particular the influence of pyrogenic carbon. Initial results for the Smithian and Spathian from sections sampled in Svalbard show an increase of polyaromatic hydrocarbons (PAHs) during the Spathian. Particularly, phenanthrene and anthracene concentrations increase amid the Smithian-Spathian boundary (SSB). These increases coincide with increased d¹⁸O_phosphate values (approx. 14 ‰ to 17 ‰) measured for conodonts in the same locality and are suggestive of a rapid cooling at the SSB. Global temperature decline in the late Smithian would decrease corresponding precipitation intensities, particularly in high latitude regions (Goudemand et al. 2019). Decreasing precipitation intensity generates much less runoff that, in turn, is associated with increases in wildfire activity in high latitude regions (Grosse et al. 2011). Increased wildfire activity may have contributed to increased atmospheric pCO₂ levels. In contrast, incomplete combustion of organic matter would also form a recalcitrant terrestrial organic carbon pool, which could act as a carbon sink.