Linkage of paleolake to climate change during the Early Permian Artinskian warming

Abstract

The linkage of paleolake to past climate change is an important but under-recognized problem of broad geological interest. Here we present a pilot study on the Early Permian Artinskian warming (ca. 290 Ma) during the Late Paleozoic Ice Age (LPIA), using comprehensive records of organic-rich fine-grained rocks in a large paleo-lake system in the mid-latitudes of Northern Pangea, i.e., the Early Permian Lucaogou Formation in the paleo-Junggar lake, one of the largest known Phanerozoic lakes. Results show that the elevated continental chemical weathering (evidenced by elevated CIA [chemical index of alteration] values) and negative carbon isotopic excursions (CIEs) in the Lucaogou Formation reveal that climate warming occurred during the Artinskian warming event. Paleoenvironmental parameters associated with climate warming such as Cu/Ti and Sr/Ba ratios and P and total organic carbon (TOC) contents exhibit synchronous changes, indicating that climate warming during the Artinskian intensified the hydrological cycle, causing an increase in riverine nutrient input and an enhancement of aquatic primary productivity. Coupled with stable salinity stratification in the lake, these processes facilitated the enrichment of organic carbon (TOC ∼5.0 %). Further evidence from the ¹³C-enriched (δ¹³C = 3.2–12.3 ‰; average = 6.1 ‰) signals in authigenic dolomites reveal that intense microbial methane cycling occurred in the lake. Moreover, the co-variation of unusually high sediment mercury concentrations with CIEs, high CIA values and TOC contents indicates that volcanism was likely the key initial factor driving climate warming and the hydrological cycle, as well as promoting the burial of organic carbon and methane release in lakes. It is estimated that ∼290 Gt of organic carbon was extracted and sequestered in the paleo-Junggar lake from the atmosphere–ocean system during ∼3 Ma. The organic carbon burial rate is estimated at ∼1 × 10¹¹ gC/yr, accounting for approximately 0.1–0.2 % of the global organic carbon burial rates over the same period, and generated ∼540 Gt of methane during the Artinskian warming. Our new insights highlight the importance of terrestrial carbon cycling during the critical geological transition intervals. The carbon sequestration in these lakes could have had a global effect, with negative feedbacks in the exogenous carbon cycle, whereas the emissions of methane contributed to global warming as a carbon source.