Orbitally paced climate–carbon-cycle interactions and spatial heterogeneity of the late Triassic Carnian pluvial episode

The Carnian Pluvial Episode (CPE; 234–232 million years ago) is an iconic but poorly understood hyperthermal event. Here, we present an integrated high resolution (~2–10 kyr) multi-proxy record from a Carnian lacustrine succession of the Junggar Basin of northwestern China. The high-resolution palaeontological, sedimentological and geochemical signals from the Dalongkou section enable the precise identification of the onset of the CPE and enhanced volcanic activity, supporting the interpretation that the rapid onset of the CPE (~15.8 kyr) could have been the result of volcanism and subsequent surface carbon-cycle feedbacks.

We employ cyclostratigraphic (magnetic susceptibility) and organic-carbon isotopic data to explore the carbon-cycle dynamics. The Earth’s orbital eccentricity periodicity originates from the beat frequencies between the secular fundamental frequencies of the perihelion precession. The (𝑔2−𝑔5) 405-kyr cycle, which mainly involves the fundamental frequencies of Venus and Jupiter, is the most stable term in a quasi-periodic approximation of the Earth’s orbital parameter. Based on the 405-kyr tuning scheme and the modulation analysis of short eccentricity terms, the CPE terrestrial carbon cycling, at a scale of ± 1‰ (δ¹³C_org), displays an in-phase relationship with the 405-kyr-long-eccentricity oscillation, i.e., the higher values of the δ¹³C_org are correlated with high eccentricity (high variance of precession), and vice versa. This relationship suggests that during eccentricity minima, cooler and more stable climates, within a generally warm background, facilitated the expansion of continental carbon reservoirs. This expansion led to greater land storage of isotopically light carbon and a corresponding rise in marine dissolved inorganic carbon (δ¹³C-DIC), with the reverse occurring during maxima. This in-phase behavior is most pronounced in the CPE interval because the 405-kyr eccentricity-related forcing signal was amplified by internal climate feedbacks of the carbon cycle under hyperthermal conditions. This result, together with previous long-term carbon isotope records, shows that such a climate–carbon-cycle interaction may have been widespread throughout the warm Mesozoic Era, including hyperthermal intervals.

In addition, we investigate the global changes in hydrological cycling during the CPE using a combination of palynological and sedimentological data, as well as Earth System modelling. Together, these data allow a comprehensive overview of climate–carbon-cycle dynamics, including potential driving mechanisms for the CPE, and coeval changes to the hydrological cycle. The CPE hydrological cycle was typified by increased aridification in continental interiors and multiple precipitation centers at low-latitude eastern regions of Pangea and at the poles. The carbon and hydrological cycle changes of the CPE include features reminiscent of other warm events, suggesting they may share key characteristics and hold important clues to Earth system functioning.