Climate–carbon-cycle interactions and spatial heterogeneity of the late Triassic Carnian pluvial episode

Domain: earth_science
Published: 2025-06-30
Editorial outcome: major_revision

Abstract
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. We find that the rapid CPE onset (~15.8 kyr) could have been the result of volcanism and subsequent surface carbon-cycle feedbacks. The CPE terrestrial carbon cycling, at a scale of ±1‰ (δ13Corg), displays an in-phase relationship with the 405-kyr-long-eccentricity parameter, paralleling the warmhouse climate–carbon-cycle interactions throughout the Oligo–Miocene. The CPE hydrological cycle was typified by increased aridification in continental interiors and multiple precipitation centres 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.

Introduction
As a typical greenhouse period in Earth’s history, the Mesozoic Era was characterised by the recurrent occurrence of global hyperthermal events1. Investigating possible tipping points, global changes and high-resolution terrestrial responses to these Mesozoic hyperthermal events will deepen our understanding of past and present carbon-cycle perturbations. The Late Triassic Carnian Pluvial Episode or CPE (~234–232 Ma) represents a warming event characterised by oceanic anoxia2–5 and significant enhancement of the hydrological cycle6,7 and continental weathering8,9. These phenomena led to significant changes to life in marine and terrestrial ecosystems3,10–12. In particular, the CPE resulted in a burst of reef growth and spread of neopterygian fishes in the sea3, as well as the radiation of terrestrial animals and plants, including dinosaurs13,14, turtles15, crocodiles16, and various modern conifers17,18. This interval is synchronous with carbon-cycle perturbations marked by one or more pronounced global negative carbon-isotope excursions (CIEs), with amplitudes of ~2–4‰11,19–24.

The emplacement of the Wrangellia Large Igneous Province (LIP) is considered a primary trigger of the CPE, likely amplified by the release of isotopically light CO₂ from surface feedbacks into the ocean-atmosphere system, driving a warmer, more humid climate and associated negative CIEs19,25,26. The identification of multiple mercury (Hg) enrichments and increased input of unradiogenic osmium (Os) in sedimentary successions encompassing the CPE support a contribution from elevated volcanic emissions26–31. Nevertheless, the Wrangellia LIP (estimated 5×1018 g C)19 alone could not have released enough isotopically light carbon to account for the magnitude (~2–4‰) of the global CIEs, as suggested by mass-balance calculations and modelling12,19,23,32. Consequently, despite evidence for volcanic emissions at the time of the CPE, climate-carbon cycle feedbacks may have been critical to the CPE.

The increased global humidity is widely considered a prominent feature of the CPE, supported by the record of higher terrigenous inputs into shallow-marine sediments and a shift from playa-lake and continental sabkha environments to rivers or freshwater lakes3 (Fig. 1 and Supplementary Text 1). However, given the lack of a high-resolution chronostratigraphic framework, the correlation between enhanced humidity on land and the CPE interval remains unclear33,34. In several regions, including the basins of the Newark Supergroup in the USA, sedimentary evidence of increased humidity during the CPE has not been identified35. In addition, records of arid events have been found in the Wessex Basin (UK)36, Central European Basin (ref. 37, but see ref. 38), and in terrigenous material (derived from aeolian dust) of a deep-sea sequence in the Inuyama area (Japan)39 (Fig. 1 and Supplementary Text 1). Therefore, the manifestation of global hydrological cycle changes during the CPE is still under debate33.

In this study, we report on a continuous lacustrine sequence (Dalongkou section) in the southern Junggar Basin, northwestern China, which provides a record of the CPE based on biostratigraphy and radiometric ages (radiometric methods in Supplementary Text 2) and allowed the construction of an integrated astronomically calibrated age model. The high-resolution palaeontological, sedimentological and geochemical signals from the Dalongkou section enable the detection of the CPE onset. Additionally, mercury (Hg) concentrations and isotope ratios, proxies for enhanced volcanic activity40, have been measured within the established astronomical timeframe. We further employ cyclostratigraphic and organic-carbon isotopic data to explore the carbon-cycle dynamics. Finally, 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.

Results
Age and stratigraphy
The Junggar Basin in the Xinjiang Uygur Autonomous Region, northwestern China, is part of the Kazakhstan-Junggar Plate. The Dalongkou section (43°58′30″N, 88°53′03″E), located on the southern margin of the Junggar Basin, represents a high-palaeolatitude (~60°N) lacustrine succession that developed during the Late Triassic41 (Fig. 1). The Huangshanjie and Karamay formations, over 500 metres thick, are continuously deposited without obvious hiatus. The Karamay Formation features significant alluvial-fan and fluvial components, with large sets of coarse sandstone and interbedded mudstone42. The conformably overlying Huangshanjie Formation consists largely of lacustrine deposits, dominated by dark mudstones, locally siltstone, sandstone, and interbedded limestone (Fig. 2a). Diverse plant macrofossils, spores, pollen, and vertebrate fossils in the Karamay and Huangshanjie formations attest to the lacustrine origin of these sediments42. The vertebrate Fukangichthys fauna and the palynological zonation (Aratrisporites, Dictyophyllidites-Aratrisporites, and Lycopodiacidites-Stereisporites) suggest that the boundary between the Middle Triassic and Upper Triassic lies between the uppermost Karamay Formation and the bottom of the Huangshanjie Formation42. The U-Pb radioisotopic dating on two sandstone samples from the uppermost Karamay and lower Huangshanjie layers shows a maximum depositional age of 234.8 ± 0.8 Ma to 232.9 ± 0.7 Ma (Fig. 2 and Supplementary Text 2), further constraining the lower Huangshanjie Formation to the lower–middle Carnian43. These absolute ages place the onset of the CPE (~234 Ma) between the Middle-Upper Triassic boundary (237 Ma) and the stratigraphic level of the sample with the youngest depositional age of 232.9 ± 0.7 Ma.

Cyclostratigraphy and chemostratigraphy
Magnetic susceptibility (MS) constitutes a sensitive proxy of lithological and environmental changes (see “Methods”). Utilising rough sedimentation rate constraints derived from age constraints (~6 cm/kyr), correlation coefficients and hypothesis testing (5-to 10-cm/kyr optimal sedimentation rate) (Supplementary Text 3), significant Milanković cycles can be discerned through time-series analysis of the MS records in the Huangshanjie Formation (Fig. 2b, c and Supplementary Text 3). The spectral analysis of the MS series indicates a series of obvious sedimentary wavelengths, i.e., ca. 34 m, 13.3 m, 10.8 m, 9 m, 8 m, 3 m and 1.6 to 1.3 m (Supplementary Text 3), approximately in accord with the ratios of the 405-kyr long eccentricity, 173-kyr obliquity, 125–95-kyr short-eccentricity, ~33-kyr obliquity and ~21–17-kyr precession cycles around 234 Ma, based on the La2004 astronomical solution44. The 405-kyr long eccentricity and 173-kyr obliquity cycles are widely regarded as metronomes for establishment of deep-time astrochronology45; therefore, the inferred 405-kyr long eccentricity (50–25 m) and 173-kyr obliquity (16.7–12.5 m) wavelengths in the MS series are tuned to the 405-kyr and 173-kyr synthetically made sinusoid, respectively. The spectral analysis of the two tuning schemes shows highly correlated astronomical signals corresponding to the 405-kyr long eccentricity, 173-kyr obliquity, and 131–95-kyr short eccentricity components, thereby confirming the reliability of the astronomical calibration (Supplementary Fig. 5). The U-Pb age of 232.9 ± 0.7 Ma was used to constraint tentatively the ~4-Myr floating astronomical timescale (ATS) tuned to the 405-kyr pure sinusoid.

We combined biostratigraphy (palynology and vertebrate fossils) and U-Pb dating to place the CPE in the lower part of the Huangshanjie Formation, and further constrained the onset of the CPE using carbon-isotope data. We present high-resolution bulk organic carbon-isotope (δ13Corg) records spanning 316.20 m, covering the top part of the Karamay Formation and the lower–middle part of the Huangshanjie Formation (~234–230 Ma, Supplementary Text 4). Our results of Rock-Eval, kerogen macerals and compound-specific (long-chain n-alkane) δ13C analyses (analysis methods in Supplementary Text 4) indicate that the bulk organic carbon-isotope record from the Dalongkou section dominantly reflects the atmospheric δ13C-CO2 signal, which reflects global carbon-cycle perturbations (Supplementary Text 4). The δ13Corg values exhibit relatively stable background values of –25‰ to –23‰ in the basal 38.00 m, followed by pronounced (∼6.5‰, 139.2 kyr) and moderate (∼3.5‰, 114.3 kyr) negative excursions at 39.50 m to 50.50 m and 60.25 m to 71.75 m, named CIE1 and CIE2, respectively (Fig. 2d, e and Supplementary Fig. 15). Additionally, we found an abrupt but relatively weak negative δ13C shift (∼1.2‰, 19.0 kyr) stratigraphically below the level of the CPE onset (CIE1, Fig. 3), which is here termed the pre-onset excursion (POE). A similar feature was first reported in the Palaeocene–Eocene Thermal Maximum46 and similar phenomena were then also identified at the Triassic–Jurassic transition47 and Cretaceous hyperthermal events (Oceanic Anoxic Event 1d48; Oceanic Anoxic Event 249). However, there remains uncertainty as to whether the underlying mechanisms are consistent across different events, and whether they represent global phenomena. Given its short-lived duration (e.g., several centuries to many millennia in the PETM and ~19 kyr for the CPE POE here)50, the POE may be present in other hyperthermal events but remains enigmatic as it can only be captured in those sections with sufficiently high sedimentation rate coupled with high-resolution analysis.

The two main CIEs in the Junggar Basin span about 374.2 kyr (Fig. 2 and Supplementary Fig. 15), which is broadly consistent with the time span (~300 kyr) of the first two CIEs recorded in the Bagong Formation of Tibet31 and the Dunscombe Mudstone Formation of England24. However, the entire CPE with episodic CIEs is generally considered to have lasted longer than 1 Myr based on cyclostratigraphy (~1.1 Myr), biostratigraphy and magnetostratigraphy (1.6 to 1.7 Myr)3,13,51. We here focus on the POE and CIE1 in order to decipher the onset mechanisms behind the CPE.

Mechanistic origin of the CPE
Mercury (Hg) concentrations and isotopes have been widely used as a fingerprint of far-field volcanic activity in both marine and terrestrial settings during the extreme climatic events in the Phanerozoic Aeon (e.g., ref. 52). To explore the possible relationship between the CPE and enhanced subaerial LIP activity, high-resolution (~14-kyr average sampling interval throughout the section and ~2-kyr sampling interval near the onset of the CPE) Hg concentrations and isotopes were measured (Supplementary Text 5), and show one Hg/TOC spike in the Dalongkou section as synchronous with the POE, with elevated Hg occurring through the CIE1 (Fig. 3 and Supplementary Fig. 15). Interestingly, the Hg/TOC spike pre-dating the CIE1, little discussed in the literature, may be widespread in Europe, South China, Tibet and Japan27,29–31, and occurs at a time of decreasing 187Os/188Os ratios recorded from far-field pelagic sections derived from the Panthalassa or palaeo-Pacific Ocean (Supplementary Fig. 16)4,28,53.

Pre- and post-POE intervals exhibit near-zero odd-Hg MIF values (mass-independent fractionation signature, most Δ199Hg values ranging from 0 to –0.04‰), whereas the POE interval itself is characterised by large ranges of odd-Hg MIF values (–0.12‰ to 0.05‰; Supplementary Fig. 15). This pattern provides evidence of a mixture of several potential sources of Hg, including terrestrial input and atmospheric deposition to the lake system during the interval of mercury enrichment40. The overall lower than volcanic (<0‰) range Δ199Hg values indicate proportionally more terrestrial Hg (e.g., organic-rich soils with Δ199Hg values of ∼ –0.25‰) imported into the lacustrine system40. However, some high Δ199Hg values also appear between the lower values, indicating that atmospheric Hg2+ transport (direct atmospheric deposition or photochemcial reduction of Hg2+) probably contributed to the mercury enrichment, thereby offsetting the low values of the terrestrial input. In short, the results point to a volcanically derived Hg anomaly just prior to and during the CPE onset.

The coincidence of the POE and concomitant volcanically derived Hg enrichment (prior to the CIE) most likely represents a pulse of volcanism that released a relatively small mass of carbon within a short interval and caused a weak warming event (Supplementary Fig. 17)47,48,54. A precursor carbon release or warming event may signal the growing instability of thermally sensitive carbon sources, potentially triggering a positive feedback loop to sustain subsequent warming (Fig. 3)50,54.

Our results show that the main carbon-isotope excursion (CIE1), which represents the CPE onset, was geologically rapid, lasting ~15.8 kyr (Fig. 3). This time interval is longer than comparable phenomena of the Triassic–Jurassic transition (1–10 kyr onset)47 and Palaeocene-Eocene Thermal Maximum (at least 4 kyr onset)55, but is shorter than the Permian–Triassic mass extinction (~40 kyr onset)56, Early Jurassic T-OAE/Jenkyns Event (~65 kyr)57, Early Cretaceous OAE1a (less than 36 kyr)58 and the Late Cretaceous OAE 2 (~80–100 kyr)49. Previous geochemical modelling results suggest that the carbon released by the Wrangellia LIP alone could not have generated the magnitude of the CIE1 (~3–4‰)20, and potential sources of additional 13C-depleted carbon are hypothesised to derive from weathering of organic-rich sedimentary rocks, thawing permafrost, or dissociation of sub-ocean-floor methane hydrates3,12,20,23. Such potential additional sources of isotopically light carbon do not constitute an isolated case for the Carnian, as most carbon emission estimations from major LIPs do not match the corresponding δ13C excursions (e.g., the Triassic–Jurassic transition47 and Palaeocene-Eocene Thermal Maximum54). Palaeotemperature reconstructions suggest relatively warm climatic conditions before the CPE, with a global mean air temperature of ~23–24°C1,59 and tropical sea-surface temperatures in eastern Tethys of ~27°C11. Under such warm conditions (Fig. 4a), the global permafrost surface area should be much smaller than that it is today60. Thus, the total amount of 12C-enriched greenhouse gases from thawing permafrost is too limited to generate the magnitude of CIE1 (Supplementary Text 6). However, a hydrate reservoir only 29% the size of the modern one (>1.05 × 10¹⁹ g C)61 could hold enough ¹³C-depleted carbon to produce a ~3–4‰ excursion in the δ¹³C of the exogenic carbon cycle (Supplementary Text 6). Therefore, the dissociation of sub-ocean-floor methane hydrates might be an important source of the isotopically light carbon released during the CIE1 (Fig. 3). Other feedback sources, such as peat and forest, could also contribute to the supply of 13C-depleted carbon.

These sequence of events, including evidence for volcanic activity followed by a large CIE may support a scenario whereby the emplacement of the Wrangellia LIP prior to the CPE induced net positive climate–carbon-cycle feedbacks. The rapid release (~15.8 kyr) of isotopically depleted carbon from surface reservoirs such as methane hydrates could help explain the large amplitude of CIE1. Such a sequence may be consistent with strong positive feedback and potential tipping point (i.e., irreversible changes in the Earth system) behaviour during the CPE. However, we recognise that this is a simplified scenario, and the complexity of the event likely reflects multiple contributing factors. Further investigation is needed to understand fully the interplay of various processes that could have shaped the CPE.

Climate–carbon-cycle interaction through the CPE
Our results provide terrestrial insights into the climate–carbon-cycle interaction on 405-kyr long-eccentricity timescales through the CPE. Here, we use the term climate–carbon-cycle interaction to describe the coupled feedback system in which climate variables (e.g., temperature, hydrology and weathering) influence carbon-cycle processes (e.g., soil respiration, net primary productivity and CO₂ solubility), while the carbon cycle, in turn, regulates global climate by modulating atmospheric greenhouse gas concentrations (CO₂ and CH₄)62,63. The orbitally driven changes in Earth’s hydrological processes and carbon cycles, occurring over tens of thousands to millions of years, form the underlying pattern of climate–carbon-cycle interactions62–64. Previous research has indicated that the climate–carbon-cycle interaction was paced by 405-kyr long-eccentricity rhythm throughout the Oligo–Miocene time interval followed by a striking phase reversal at 6 Ma, signalling a reorganisation of the climate–carbon-cycle system in response to coldhouse conditions63. 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 maxima63.

Our results reveal the pronounced in-phase variation between the filtered long-eccentricity cycles and the amplitude modulation of short eccentricity in the MS series over the CPE. This relationship suggests that the higher values of the filtered eccentricity cycles are correlated with high eccentricity (corresponding to high variance of precession), and vice versa (Fig. 2b). Remarkably, the calibrated δ13Corg fluctuations are paced by 405-kyr long-eccentricity rhythm, on the scale of ±1‰ (Fig. 2e, f). Therefore, the climate–carbon-cycle interaction exhibits in-phase behaviour between the terrestrial δ13Corg series and 405-kyr long-eccentricity cycles during the CPE (Fig. 2). This in-phase behaviour is most pronounced in the CPE interval because the 405-kyr eccentricity-related forcing signal was amplified by internal climate feedbacks (e.g., enhanced seasonal differences, Supplementary Text 7) of the carbon cycle under hyperthermal conditions62 (Supplementary Text 3).

In conclusion, our findings show that the CPE terrestrial carbon cycling, at a δ13Corg scale of ±1‰, displays an in-phase relationship with the 405-kyr long-eccentricity metronome, which appears similar to the warmhouse climate–carbon-cycle present throughout the Oligo–Miocene interval63. This result, together with previous long-term carbon-isotope records64,65, show that such a climate–carbon-cycle interaction may have been widespread throughout the warm Mesozoic Era, including hyperthermal intervals. Therefore, this climate–carbon interaction may be the norm after the emergence of vascular plants, whereas the coldhouse climate–carbon-cycle dynamics of the earliest Pliocene may represent a more unusual situation.

The hydrological cycle during the CPE
Our palynological results show an arid and warm climatic state in the Junggar Basin during the δ13Corg fluctuations over the interval extending from the POE to the CIE2 (Supplementary Text 8 and Supplementary Fig. 15). Over this interval, the sediments exhibit a substantial decrease in hygrophytic elements (e.g., Leiotrilete and Todisporites) from averaging 22% down to ~10%. Our AWI-ESM simulations confirm a more arid and warmer climate during this interval in the Junggar Basin (Fig. 4b).

Our results show that precipitation changes during the CPE exhibited spatial heterogeneity, accompanied by a poleward shift of pre-existing precipitation zones and no evidence for global humidification. The heterogeneous pattern of precipitation changes is characterised by predominantly increased precipitation near the Equator and at high latitudes, while subtropical latitudes exhibit diminished rainfall (Fig. 4b). Moreover, mountains and extensive continental areas can block moisture transport, resulting in enhanced net evaporation within the interior of supercontinents (Pangaea)47. In contrast to previous hypotheses regarding unusual global humidification during the CPE2,7,13,26, the integrated stratigraphy and Earth system model highlight the spatial variations in global precipitation patterns, characterised by increased aridification in continental interiors and the emergence of multiple precipitation centres in low-latitude eastern continents and polar regions, including the Arctic, northeastern Tethys, northeastern Gondwana, and the Antarctic (Fig. 4b). These precipitation changes are corroborated by geological records throughout the CPE (e.g. the progradation of the largest delta system in geological history in the Boreal Ocean and the westward migration of its main depocenter66; the large-scale increase of terrigenous inputs and the extinction of carbonate platforms in the southwestern Tethys continental shelf67,68 and South China11,69) (Fig. 1). Our modelling of annual global changes, consistent with other palaeoclimatic simulations32,70,71, is unable to the wetter climate in the western and northwestern Tethys as indicated by previous sedimentological evidence (e.g., refs. 3, 51). The remaining proxy–model differences may be due to unresolved local features in precipitation or the implementation of palaeotopography. Nevertheless, the newly proposed pattern appear to largely conform to established hydroclimate features observed in other past warm periods72, thereby amplifying the spatial heterogeneity in precipitation distribution.

Implication for understanding past hyperthermal events
Understanding climate–carbon-cycle interactions and tempo of past hyperthermal events is essential to accurately project the consequences of anthropogenic carbon emissions. Our findings suggest that the CPE shares key features and perhaps driving mechanisms with several other hyperthermal events including the Triassic–Jurassic hyperthermal event, Cretaceous OAEs, as well as the Palaeocene–Eocene Thermal Maximum. Although these hyperthermal events commonly lasted up to a few million years, the onset of each appears geologically rapid, lasting 1–20 kyr, and may be consistent with a net positive feedback response of the climate–carbon-cycle to elevated volcanic carbon dioxide emissions. Moreover, during the hyperthermal events, different regions may have experienced periods of extreme drought or severe flooding, reflecting the contrasting extremes of climate. Thus, despite differences in nomenclature, these events share a fundamental nature as hyperthermal episodes. These similarities suggest that understanding their commonality might hold essential information on the nature of hyperthermal events and specifically which elements in the climate and carbon cycle contribute to these anomalously warm periods.

Methods
δ13Corg and TOC
Both organic-carbon isotopes (δ¹³Corg) and TOC contents were analysed for a total of 289 samples at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences. Samples were trimmed to remove visible veins and weathered surfaces and ground using a sample crush (Vibratory Disc Mill RS200) for geochemical analyses. One gram of homogenised sample was placed in a polypropylene Falcon tube and decarbonated overnight with 3 molar HCl for 24 h. This process was repeated at least three times to ensure the complete removal of carbonates. The carbonate-free residual powder was rinsed 4 times with Milli-Q water to reach neutral pH. Samples were then dried at 60°C in an oven. Dry samples were crushed, loaded into capsules, and then flash-combusted at 1060°C in an Organic Elemental Analyser (FLASH, 2000) fitted with a zero blank autosampler. The carbon-isotope composition and TOC content (wt%) of generated CO2 were measured by a thermal conductivity detector and Delta V Advantage Isotope Ratio Mass Spectrometer, respectively. All isotope data are reported in per mil (‰) variation relative to the Vienna Pee Dee belemnite (VPDB) standard. Calibration of δ13Corg values was accomplished using a working standard B2151 (δ13Corg = −26.27‰), GBW04407 (black carbon, δ13Corg = −22.43‰) and Urea (δ13Corg = −39.79‰). The analytical uncertainty for TOC was calculated as a relative error of less than ±5%, and the standard deviation for δ13Corg was ±0.2‰ (1σ), both determined through replicate analyses of standard samples.

Mercury concentrations
Hg concentrations were analysed using a Direct Mercury Analyser (DMA80) at the China University of Geosciences (Wuhan). About 150 mg for siltstone/limestone samples and 100 mg for mudstone samples were used in this analysis. Results of low and high Hg were calibrated to the GBW07424 (33 ± 4 ppb Hg) and GBW07403 (590 ± 80 ppb Hg) standards, respectively. One replicate sample and a standard were analysed for every ten samples. Data quality was monitored via replicate multiple analyses of GBW07424 and GBW07403, yielding an analytical precision (2σ) of ±0.5% of reported Hg concentrations.

Mercury isotopes
Hg isotopes were analyzed at the State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang. The analysis of Hg-isotopic compositions followed the procedures described in ref. 73. Hg was extracted and concentrated using the double-combustion and trapping dual-stage protocol73. The NIST SRM 997 thallium was used for mass-bias correction, the international Hg standard NIST SRM 3133 was used as an isotopic ref. 73, and the NIST RM 8610 (UM-Almaden Mono-Elemental Secondary Standard) was used as the reference material as a secondary laboratory Hg standard (National Institute of Standards and Technology, Gaithersburg, USA). Procedural blanks were negligible (<0.13 ng, n=8) relative to the amount of Hg in samples (>20 ng). Good recovery (98 ± 4%, 2SD) guarantees that no Hg-isotope fractionation occurred during the pre-concentration procedure. Volatile ionised Hg0 generated by SnCl2 reduction in a cold-vapour generation system was introduced into the plasma (Nu-MC–ICP–MS) with Ar as a carrier gas. Hg-isotopic results are expressed as delta (δ) values in per mil (‰) variation relative to the bracketed NIST 3133 Hg standard, as follows74:

δxxxHg = [ (xxxHg/198Hg)sample / (xxxHg/198Hg)standard - 1 ] × 1000‰ (1)

Any Hg-isotope composition that did not follow the theoretical MDF was considered an isotopic anomaly caused by MIF. MIF values are indicated by capital delta (Δ) notation (in per mil) and predicted from δ202Hg using the following equations74

Δ199Hg = δ199Hg - 0.252 × δ202Hg (2)

Reproducibility of Δ199Hg was better than ±0.05‰ (2σ).

Elemental analyses
Major and trace elements were analysed for a total of 154 samples at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences. An ~50 mg of sample powder was weighed and ashed at 110°C for 3 h. Then, the sample powder was digested in 1 ml of HNO3 and 1.5 ml of HF at 190°C for 72 h. After cooling, samples were evaporated at 115°C to incipient dryness, then 1 mL HNO3 was added and the sample was dried again. This process was repeated at least three times to ensure the complete removal of HF. The resultant salt was re-dissolved with 1 ml HNO3 and 2 ml Milli-Q water before it was again sealed and heated in the bomb at 190°C for 12 h. After completing digestion, these solutions were analyzed for the target elements on a quadrupole inductively coupled plasma mass spectrometer (ICP-MS) and ICP optical emission spectrometer. Two standards (SDO-1, SRM 88b) were used to monitor the analytical reproducibility. Precision and accuracy for major and trace elements are estimated to be better than 5% and 1%.

Astronomical cycles
The total 1095 samples for the magnetic susceptibility (MS) experiment were cleaned to remove weathered surfaces and broken into small pieces of ~1–2 mm3, then filled with 8-cm3 non-magnetic (plastic) sample boxes. All samples were analyzed on the Kappa Bridge Magnetic Susceptibility System (sensitivity: 3 × 10–8 SI) at the State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences. Then, all samples were weighed by an electronic balance, with a mass accuracy of 10–4 g. The mass magnetic susceptibility (χ) was calculated by the ratio of the measured volume magnetic susceptibility (κ) to rock density. In a relatively humid environment, ferromagnetic minerals such as magnetite and maghaemite imply relatively high MS values, while in a relatively arid environment, carbonate deposits and coarse clastic rocks have relatively low MS values due to the diamagnetism of carbonate and quartz75. The obtained MS series (χ) were interpolated with a main sampling interval of 0.25 m. To strengthen the orbital signals, we clipped values larger than 8.5 × 10–5 (cm3/g), and then detrended the series by removing linear trend. We analyzed the periodicity of the untuned and tuned MS series by the Multitaper Method (MTM)76 and Evolutionary Fast Fourier Transform77 spectra. The correlation coefficient (COCO) and null hypothesis testing (H0SL)78 were applied for quantitatively tracking of the sedimentation rates. In the two tuning schemes, the 50–25 m (0.02–0.04 cycles/m) wavelengths filtered via a Gaussian filter and the 16.7–12.5 m (0.06–0.08 cycles/m) wavelengths filtered via a Taner filter are tuned to 405-kyr and 173-kyr synthetically made sinusoids, respectively. The 405-kyr tuning scheme is used to establish a floating astronomical timescale, which is further constrained by the U-Pb age of 232.9 ± 0.7 Ma. The time-height mode is based on the calibration of the peaks of the filtered curve. In the time domain, the long and short eccentricity cycles were filtered by Gaussian (0.0019–0.003 cycles/kyr) and Taner (0.0075–0.0115 cycles/kyr) filters, respectively. The Hilbert transform was used to extract the amplitude modulation of the filtered short eccentricity cycles. The δ13Corg series is calibrated to the time domain based on the 405-kyr tuning scheme with the values below –25.5‰ clipped in order to highlight fluctuations forced by eccentricity, on the scale of ±1‰. Continuous wavelet transform was used to examine the periodicity of the tuned MS series and calibrated δ13Corg series (values clipped below –25.5‰). The proportion of hygrophyte was calibrated to the time domain based on the age model of the established ATS. All of the time-series analyses were conducted using Acycle 2.879.

Model simulations
To examine the spatio-temporal changes in temperature and precipitation during the CPE, we performed climate simulations using AWI-ESM80. AWI-ESM is a coupled ocean-atmosphere model widely used in palaeoclimate research. The land-sea distribution and topography is applied from the reconstructed palaeo-digital elevation model41 from 235 million years ago. There is no continental ice sheet. The ocean component of AWI-ESM employed an unstructured triangle mesh with horizontal resolution ranging from 30~270 kilometres (Supplementary Fig. 18), whereas the atmosphere component used a consistent horizontal resolution of 3.75o × 3.75o. We performed climate simulations under different atmospheric CO₂ levels, i.e., 568, 1136, 1704, and 2272 ppmv. At the end, the 568 ppmv experiment is used as an analogue of the climate prior to the CPE, while the 1704 ppmv experiment is used to mimic the relatively warmer climate during the CPE. Two criteria were used in the selection process: first, the selected CO2 levels are close to the proxy-based reconstruction of atmospheric CO2 before and during the CPE81; second, the simulated global mean surface temperatures are close to those previously reconstructed1,41. A similar approach was also applied in previous studies to reconstruct the deep-time Earth’s climate71,82. It should be noted that the simulated climate change patterns in greenhouse climates do not differ much depending on the CO2 level. Differences in CO₂ levels primarily affect the amplitude of climate changes. All other boundary conditions, such as solar constant and Earth’s orbit, were kept the same as the pre-industrial era, unless specifically stated. The 568 ppmv experiment was run for 2000 years to allow the climate system to reach a surface equilibrium state. The 1704 ppmv experiment, initialised from the first experiment, was run for 1000 years. This procedure allows the upper ocean and surface climate to achieve an equilibrium state. The last 100 years of the two experiments were used for comparison.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The Carnian Pluvial Episode has gained increasing research interest in recent years. It represents a type of crisis rarely seen in the Phanerozoic. Zhao et al. provide a multi-proxy study on a mid-latitude lake succession. Contrary to the general conception that the climate shifted towards more humid conditions, the authors suggest increased aridity in continental interiors.\nI don’t see major issues with this manuscript. However, some revisions would significantly improve this manuscript. These include: 1) a better separation of results and discussion; 2) verify the modelling output. E.g., give a comparison of simulated equatorial SST with published proxy-derived records; 3) reconsider the marine methane hydrate scenario—I don’t see the necessity to include such speculation, and it is detached from the main story; 4) include critical information in the method. For example, there is a lack of explanation of pCO2 prescriptions (568 to 1758 ppm) for the CPE modelling. Inform the audience why these numbers were chosen. The analytical uncertainty of TOC and C and Hg isotope analyses are also missing.\nI understand that some coauthors are experts on Mesozoic and Cenozoic hyperthermals/climate changes. However, there are quite some mentions of Triassic-Jurassic, Cretaceous OAEs, PETM, Oligo-Mio, and sometimes Carboniferous. These barely relate to this study (late Triassic) and, when appear so often, are distractions to the central theme of this manuscript. Nevertheless, all these are fixable and should not tarnish the overall quality of this manuscript.\nCollectively, this is a comprehensive study combining the merits of multi-proxy geochemical records, high-precision geochronology and Earth system modeling. It will enhance our understanding of the CPE, and I recommend revising it before its formal publication.\nSpecific comments:\nLine 32, “non-coldhouse climate” is not a very good term to me. Is non-coldhouse equal to warm house?\nLine 35, not very clear what are the “eastern continents”. There was one continent at the time—the Pangea. I am not aware of any Carnian succession in either pole.\nLine 47, the word “remarkable” should be avoided in scientific writing.\nLine 56 the words in brackets are redundant and probably not entirely accurate. What is left today as the Wrangellia LIP was only a fraction of its original size.\nLines 77-78 I would change to “the manifestation of global hydrological cycle changes” ….\nLines 129-137 These are discussions rather than results. One might consider moving these words to later chapters.\nLines 119-121 Rock Eval analysis is not described in the method.\nLine 140-141 mis-citations of references\nLine 147, not easy to follow here. of the CPE?\nLine 179, I would delete the example. Methane hydrates are too speculative for the Carnian case and there is no evidence for it.\nLines 188-190, this is not an isolated case for the Carnian. As a matter of fact, most carbon emission estimations from major LIPs do not match corresponding d13C excursions.\nLine 194 GMAT of 23-24 represents a significant warm interval. This sentence also miscites literature. These estimated GMATs are compiled and should be used with great caution if cited this way.\nLines 194-195, ambiguous. Under what specific conditions do the authors refer to as? What is the GMAT that AWI-ESM gives in this study?\nLines 199-204, The argument is not convincing. Yes, the dissociation of marine methane hydrates could account for the d13C excursion, but there is no evidence for such events. A decrease in d13C can be triggered in a few scenarios, e.g., a decrease in primary productivity, less burial of organic carbon etc. What is the reason the methane hydrate scenario stands out in the Carnian case?\nLines 208-209 yes, this is a simple explanation but not necessarily represent the whole picture.\nLine 226, I don’t follow the symbol “↑” .\nLines 243-245, I couldn’t follow the argument here. What does “climate-carbon-cycle interaction” really mean here? Carbon cycle is always coupled with the global climate.\nLines 245-247, My apologies for not following the argument here. The sentence is grammatically incorrect to me. What does the “last 6 Myr” refer to? and how does the Carboniferous example relate to this study (late Triassic)?\nLines 255-257, this lengthy part can be revised to “Our AWI-ESM simulations confirms a ….\nLine 262 “poleward shift of precipitation patterns” is not a proper description and it’s hard to guess what the authors mean.\nLine 263 reword this sentence. Mountains can block moisture transport.\nLines 258-281 This paragraph could be improved after a proper rewrite.\nLines 295-297 Colleagues working on modern climate change won’t be fond of such a statement.\nLine 542 what is a Retsch RS200? I guess it is a rock saw.\nLine 554 in per mille (‰) relative to ……\nLine 557 Reproducibility and repeatability of\nLine 582 delete units of\nLine 587 There is no mention of the reproducibility of Hg isotopes.\nLine 612 “the” change to a\nLine 651, I don’t follow the statement here. Solar luminosity and ice coverage of the Carnian world (ice-free) should differ significantly from the pre-industry world (iced world). Revise to clarify this unambiguity.\nLines 655, 658 I don’t follow the term “quasi-equilibrium”, i.e., the simulations did not reach equilibrium?\nLine 657, 1000 model year is really low. Did the simulation collapse?\nFigures:\nFig. 2 the black shaded parts in the log stand for black shales, do they? I didn’t see any black shale in the field photo (Fig. S1). Maybe include some better field photos.\nThere are both extended data figures and supplementary figures (in the supplementary materials). The two systems are not very easy to follow.\nExtended Data Fig. 3 The Tibetan record is very poor, and is not a good case to correlate. Ref 30 gave a d13Carb value lower than -5 per mille and down to almost -10 per mille. This cannot be true for any normal marine carbonate. The numbers might have measured from carbonate cements in sandstone or diagenetically highly altered carbonates.\nSupplementary materials:\nText S2-strangely, the U-Pb dating was not included in the Method but in the supplementary.\nFig. S8 (and other log figures) Mud/Sha is better to spell in full.\nText S4 Compound-specific carbon isotopes are not mentioned in the main text.", "reviewer_2": "The manuscript by Zhao et al. provides a new record of the CPE from the lacustrine Junggar Basin in northwestern China. This manuscript presents multiple data, including magnetic susceptibility, U-Pb age, C and Hg isotopes, elemental geochemistry, and palynological data, combined with Earth System modelling, to discuss potential driving mechanisms for the CPE, and coeval changes to the hydrological cycle. Overall, the methods are appropriate and the data are valuable. However, some important issues need to be addressed before it can be considered. My main suggestions are the following:\nMajor comment\n1. Due to the lack of volcanic rocks in the study strata, the authors only determine the age using tuffaceous sandstone. The authors need more description how did your research identify Carnian Pluvial Episode? The CPE does not only mean carbon isotope excursion.\n2. Please provide more discussions concerning spores and pollen in the manuscript. How to evaluate the contribution of eolian activity on palynological compositions? If the eolian activity is strong, the spores and pollen could be derived from other distant regions (not surrounding regions). Please clarify it. Besides, I strongly suggest that the authors add climate status in Extended Data Fig. 2. Since the authors have measured elemental content, I strongly suggest that they use geochemical proxies (e.g., CIA) to reconstruct climate evolution in the study area.\n3. Lines 122-126: The studied section displayed a CIE with an amplitude of 6.5‰, which is larger than coeval sedimentary successions (lines 52-54). Lines 202-204: the authors suggest that the isotopically light carbon released during CIE1 may have mainly originated from dissociation of sub-ocean-floor methane hydrates. If it is true, both marine and lacustrine should exhibit a similar amplitude of carbon isotope excursion. Please clarify it.\n4. Lines 126-129: It is recommended to define the CPE onset because CPE is Carnian Humid Episode, but not only carbon isotope excursion.\n5. Lines 124, 127 and 138: The paper is astronomically tuned based on the long eccentricity cycle (405 kyr). However, the time intervals of CIE1, CIEs, and POE discussed in the text are significantly shorter than 405 kyr, such as \"139.2 kyr,\" \"19 kyr,\" and \"374.2 kyr.\" This may lead to unreliable results for these age data. It is suggested that the authors employ certain methods to minimize errors or discuss and present the magnitude of the errors.\nMinor comment:\n1. Lines 82-84: The author stated that they provided high-resolution palaeontological, sedimentological and geochemical data from the Dalongkou section to reconstruct of the structure of the CPE onset. However, detailed sedimentological description is completely missing in the manuscript. Additionally, the coordinate of the studied section needs to be added in the Geological setting.\n2. Line 140: The study of the Bagong Formation on the Qinghai-Tibet Plateau should be 30 of your references; Rather than 23, 23's study was a cyclostratigraphy study conducted by Miller et al., 2017 on a well in the UK;\n3. Lines 154-456: It seems that elevated Hg occurred before the CPE onset (Extended Data Fig. 2). Besides, the vertical variation of δ13Corg and Hg/TOC in Fig 3 and Extended Data Fig. 2 is different, please unify it.\n4. Line 541: provides detection limits and accuracy of δ13Corg and TOC;\n5. Line 568: Detection limit and accuracy of mercury isotope.\n6. Fig. S1: Please exhibit clearer filed photos in Fig. S1b and c. Besides, it is recommended to add the micrograph of tuffaceous sandstone.\n7. Extended Data Fig. 3: The red dashed line (the onset of Volcanism) is placed before the rise in Hg/TOC, but the data for Central Japan seems not to align with this. So, some adjustments may be needed.\n8. Although the English text is understandable, it can and should be improved to meet the journal's standard.", "reviewer_3": "Review of ‘Climate–carbon-cycle interactions and spatial heterogeneity of the Carnian Pluvial Episode (Late Triassic)' by Zhao et al.\nIn this manuscript, Zhao et al. investigate the Carnian Pluvial Episode (CPE), a major climate change that occurred around 234 to 232 million years (Ma) ago. The study examines climate and carbon-cycle dynamics during the CPE using high-resolution multi-proxy data from a lacustrine succession in the Junggar Basin, northwestern China. The findings highlight the rapid onset of the CPE, potentially driven by volcanism and carbon-cycle feedbacks, as well as the in-phase relationship between terrestrial carbon cycling and orbital eccentricity. Changes in precipitation patterns across different latitudes are also discussed, highlighting the spatial complexity of the CPE and its diverse regional impacts.\nThe topic developed in the manuscript is of interest to the international scientific community, contributing to research on the CPE and its links to other warm events in Earth's history. While the study provides important insights into global climate–carbon-cycle interactions and the heterogeneous nature of the CPE, some aspects of its findings align with recent studies (e.g., Dal Corso et al., 2024; Zhang et al., 2024), making its novelty appear limited. Nonetheless, this study addresses gaps in the terrestrial record of CPE, where dating limitations often restrict detailed links to the CPE. Also, its multidisciplinary approach and focus on mechanisms driving the CPE's rapid onset offer valuable insights into this poorly understood climatic event. However, the text is wordy in some parts, contains several typos, and needs major revisions (rephrasing and rewriting) for clarity and presentation. I have provided a list of comments and suggestions, organised by line number, that the authors should address.\nComments on the main text of the manuscript\nLine 46: Please cite the recent article by Lin et al. (2025) (DOI: https://doi.org/10.1016/j.marpetgeo.2025.107289) on deoxygenation preceding the CPE in the Qiangtang Basin. The findings on the environmental, paleoceanographic, and organic matter controlling processes preceding the CPE and the role of sedimentary organic matter in the global carbon cycle are relevant to your work and could be included in your discussion.\nLine 48: Please fix the typo: 'phenomana' to 'phenomena'\nLine 55-59: The sentence could be rephrased for better clarity and flow. For example:' The emplacement of the Wrangellia Large Igneous Province (LIP) (few basalts were submarine; most were subaerial) is considered a primary trigger of the CPE, likely amplified by the release of isotopically light CO₂ from surface feedbacks into the ocean-atmosphere system, driving a warmer, more humid climate and associated negative CIEs.'\nLine 70: Please include the CPE record from the Miankuhi Formation, Turan Plate (NE Iran) based on Mazaheri-Johari et al. (2021, 2022) in both Text S1 and Fig. 1. Also, add the following references to the reference section:\n- Mazaheri-Johari et al. (2021), DOI: https://dx.doi.org/10.13130/2039-4942/15646\n- Mazaheri-Johari et al. (2022), DOI: https://doi.org/10.1016/j.palaeo.2021.110777\nLine 70-72: I recommend refining the sentence for clarity, for example: 'However, given the lack of high-resolution chronostratigraphic framework, the correlation between enhanced humidity on land and the CPE interval remains unclear.'\nLine 72-74: The sentence has a convoluted structure. I suggest rewriting it, for example:' In several regions, including the basins of the Newark Supergroup in the USA, sedimentary evidence of increased humidity during the CPE has not been identified.'\nLine 81: The reference to 'Supplementary Text 2' in the sentence could lead to confusion as it could be interpreted as covering both biostratigraphy and radiometric age information. Since it focuses on U-Pb dating methodology, I suggest rephrasing it to 'radiometric methods in Supplementary Text 2' for clarity.\nLine 82: This sentence is wordy and needs rephrasing, for example: ‘The high-resolution palaeontological, sedimentological, and geochemical signals from the Dalongkou section enable the detection of the CPE onset.’\nLine 90: Add a comma after the word 'together'\nLine 102: The sedimentary wavelengths mentioned in the main text ('11 to 8 m') differ slightly from those in Supplementary Text 3 ('10.8 to 9 m'). Although the use of 'ca.' allows some flexibility, it would be better to justify these differences to ensure consistency and avoid confusion.\nLine 110: The phrase 'high quality of our astronomical calibration' is somewhat subjective. It would be more appropriate to describe the calibration in terms of its reliability and precision. Please consider rephrasing it.\nLine 110: 'shows' instead of 'show'\nLine 127: Please fix the typo: 'stratigrapically' to 'stratigraphically'\nLine 141: Please consider rephrasing, for example: 'However, the entire CPE with episodic CIEs is generally considered to have lasted longer than 1 Myr based on cyclostratigraphy (~1.1 Myr), biostratigraphy and magnetostratigraphy (1.6 to 1.7 Myr).\nLine 171: Please fix the typo: 'redcution' to 'reduction'\nLine 176-180: Please consider rephrasing, for example: 'A precursor carbon release or warming event may signal the growing instability of thermally sensitive carbon sources, such as sub-ocean-floor methane hydrates, potentially triggering a positive feedback loop to sustain subsequent warming.'\nLine 194: Please add 'a' before 'global mean'\nLine 203: Please add 'the' before 'dissociation'\nLine 210: Change the punctuation: 'i.e.' to 'i.e.,'\nLine 211: Please add 'the' before 'Earth system'\nLine 211: Eliminate the preposition 'to' before 'the CPE'\nLine 215-218: Please consider rephrasing, for example: 'The orbitally driven changes in Earth's hydrological processes and carbon cycles, occurring over tens of thousands to millions of years, form the underlying pattern of climate-carbon cycle interactions.'\nLine 218-222: The sentence needs to be rephrased for better readability.\nLine 219: Please fix the typo: 'rhtthm' to 'rhythm'\nLine 222-226: Please break down the sentence and consider re-phrasing, for example: 'During eccentricity minima, cooler and more stable climates, within a generally warm background, facilitated the expansion of continental carbon reservoirs. This 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.'\nLine 227-231: Please split the sentence and rephrase it.\nLine 229: 'suggest' instead of 'suggests'\nLine 246: Please add a comma before the word 'whereas' and apply this comment elsewhere in the text.\nLine 247: Please change the punctuation 'e.g.' to 'e.g.,'\nLine 254: Correct your spelling for the word 'approximatelly'\nLine 265: Typo: change the 'northestern' to 'northeastern' and apply this comment elsewhere in the text.\nLine 275: Please add 'the' before the word 'implementation'\nLine 484: 'volcanic' instead of 'volcanics'\nLine 494: Please add 'the' before the word 'proportion'\nLine 517: Please add a preposition (an or the) before the word 'expansion'\nLine 520: The ‘Geological Setting’ is often treated as a standalone section, separate from ‘Methodology’ because it provides critical context for the study area, which is important for interpreting results and is not typically considered part of the experimental or analytical procedures.\nLine 525: Please change the spelling: 'meters' instead of 'metres'\nLine 525: Replace 'Formations' with 'formations' here and elsewhere in the text.\nLine 541: There is structural issue in this section. The sentence ‘Organic-carbon isotopes and TOC contents (n = 289) were analyzed at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences\" appears misplaced because it interrupts the logical flow of the sample preparation and analysis steps.\nLine 543: Clarify what ‘n = 289’ refers to (e.g., total sample numbers) and specify if it applies to δ¹³Corg, TOC, or both.\nLine 552: 'Were measured' instead of 'was measured'\n590: Ensure the methodology section is structured consistently across all analyses for clarity and readability (e.g., state the place of analysis, the number of samples analyzed, the procedure, and the analytical precision).\nLine 591: Please fix the typo: 'power' to 'powder'\nLine 591-592: I recommend re-phrase the sentence as follows: 'Then, the sample powder was digested in 1 ml of HNO3 and 1.5 ml of HF at 190°C for 72 h.'\nLine 632: Correct the word 'ime'\nLine 650: Correct the word 'temperatue'\nLine 659: Correct the word 'comparision'\nLine 692: Correct the word 'dicussions'\nLine 702: 'work' instead of 'works'\nComments on figures:\nFig. 1: Please include the CPE record from the Miankuhi Formation, Turan Plate (NE Iran) based on recent study by Mazaheri-Johari et al. (2021, 2022).\nFig. 3: The figure caption states that 'S2: the Wrangellia LIP began releasing isotopically light carbon, POE appeared, and temperatures started to rise,' but the figure lacks any temperature data/profile to support this. Since the manuscript includes palynological studies suggesting a warm, arid climate during the δ¹³Corg fluctuations (POE to CIE2), it would be helpful to include temperature-related data in the figure or clarify how the temperature rise is being represented (e.g., using supporting data from previous studies).\nFig. 3: show 'CIE interval' in the figure.\nFig. 4: Please mark the study area (Junggar Basin) on the figure (e.g., with a star) to clarify the climate state in this basin before and during the CPE.\nComments on Supplementary Info.\nTable of Contents, Text S7: Correct the word ‘temperal’\nLine 1: 'references' instead of 'reference'\nLine 1: Eliminate the preposition 'on'\nLine 55: Correct the words 'sandston' and 'sampless'\nLine 65: 'was analyzed' instead of 'were analyzed'. Also apply the comment to line 70.\nLine 92: Please add 'the' before 'Sliding window'\nLine 93: Consider changing the verb form: 'are' instead of 'is'\nLine 131: Correct the words 'amplifing'\nLine 134: Correct the words 'eccenteicity'\nLine 138: Change the preposition: 'to the' instead of 'the'\nLine 141: 'intervals' instead of 'interval'\nLine 249: Change the punctuation: 'e.g.,' instead of 'eg.,'\nLine 265: Please add 'the' before the word 'potential'\nLine 275: 'Fig. S13' instead of 'Fig. S12'\nLine 277: Change 'on sample' to 'one sample'\nLine 278: Please consider re-phrasing, for example: 'Previous studies have shown that Hg behavior is non-linear with host-phase abundance, resulting in elevated normalized Hg values when host phase abundance is low (e.g., low TOC or low TS).'\nLine 313: Correct the word 'measureable'\nLine 347: Remove the colon after the word 'including'\nLine 573: Correct the word 'Cretaceousi'"}, "author_response": "Reference: NCOMMS-24-80380-T\nTitle: Climate–carbon-cycle interactions and spatial heterogeneity of the Carnian\nPluvial Episode (Late Triassic)\nJournal: Nature Communications\nWe thank the referees for their helpful comments that have greatly improved the\nquality of our interpretation and discussions of the Carnian Pluvial Episode. We have\nrevised the paper in line with these comments, focusing on evidence and discussion\nfor identification of the CPE in the section, addressing uncertainty/error in both\ngeochemical data and dating, verifying the modelling output and improving\ndiscussions around other records from this period. We outline detailed responses to\nindividual comments below.\nReviewer 1:\nThe Carnian Pluvial Episode has gained increasing research interest in recent years. It\nrepresents a type of crisis rarely seen in the Phanerozoic. Zhao et al. provide a multi-\nproxy study on a mid-latitude lake succession. Contrary to the general conception that\nthe climate shifted towards more humid conditions, the authors suggest increased\naridity in continental interiors.\nI don’t see major issues with this manuscript. However, some revisions would\nsignificantly improve this manuscript. These include: 1) a better separation of results\nand discussion; 2) verify the modelling output. E.g., give a comparison of simulated\nequatorial SST with published proxy-derived records; 3) reconsider the marine\nmethane hydrate scenario—I don’t see the necessity to include such speculation, and\nit is detached from the main story; 4) include critical information in the method. For\nexample, there is a lack of explanation of pCO prescriptions (568 to 1758 ppm) for\nthe CPE modelling. Inform the audience why these numbers were chosen. The\nanalytical uncertainty of TOC and C and Hg isotope analyses are also missing.\nI understand that some coauthors are experts on Mesozoic and Cenozoic\nhyperthermals/climate changes. However, there are quite some mentions of Triassic-\nJurassic, Cretaceous OAEs, PETM, Oligo-Mio, and sometimes Carboniferous. These\n1\nbarely relate to this study (late Triassic) and, when appear so often, are distractions to\nthe central theme of this manuscript. Nevertheless, all these are fixable and should not\ntarnish the overall quality of this manuscript.\nCollectively, this is a comprehensive study combining the merits of multi-proxy\ngeochemical records, high-precision geochronology and Earth system modeling. It\nwill enhance our understanding of the CPE, and I recommend revising it before its\nformal publication.\nReply: We feel great thanks for your professional review that have greatly improved\nthe quality of our descriptions and interpretation. According to your nice suggestions,\nwe have made extensive corrections to our previous draft. Hopefully we have\naddressed all of your concerns. The detailed corrections and responses are listed\nbelow.\n[1] a better separation of results and discussion.\nReply: Thank you for your suggestion. We have chosen to combine the \"Results\"\nand \"Discussion\" sections to maintain a clear and direct link between our findings and\ntheir interpretation, which we believe enhances the flow of the paper. This structure is\ncommonly used in Nature Communications. However, we are open to revising if the\neditorial team prefers a separate presentation.\n[2] verify the modelling output. E.g., give a comparison of simulated equatorial SST\nwith published proxy-derived records.\nReply: Thank you very much. We compare the simulated annual SST of eastern\nTethys (South China) with the oxygen isotope records from conodont apatite of South\nChina. Please see the Fig. S19 in the supplementary information.\n[3] reconsider the marine methane hydrate scenario—I don’t see the necessity to\ninclude such speculation, and it is detached from the main story.\nReply: Thank you for your comment. Our Hg concentrations and carbon isotopes data\nsuggest that the CIE1 at the onset of the CPE was not directly caused by volcanic\neruptions, but rather by the release of light carbon from sources unrelated to the\nvolcanism. These sources may include marine methane hydrate, terrestrial vegetation,\npermafrost and peat. We propose that the total amount of methane released could\nprovide the carbon required for CIE1, without excluding contributions from other\n2\ncarbon sources. We believe this hypothesis is helpful to understanding the early stages\nof the CPE.\n[4] include critical information in the method. For example, there is a lack of\nexplanation of pCO prescriptions (568 to 1758 ppm) for the CPE modelling. Inform\n2\nthe audience why these numbers were chosen.\nReply: Thank you very much for pointing out this issue. We have previously tried\nsimulations with CO forcings of 568 (2xCO ), 1136 (4xCO ), 1704 (6xCO ), and\n2 2 2 2\n2272 (8xCO ) ppm. At the end, the 568 ppmv experiment is used as an analogue of\n2\nthe climate prior to the CPE, while the 1704 ppmv experiment is used to mimic the\nrelatively warmer climate during the CPE. Two criteria were used in the selection\nprocess: first, the selected CO levels are close to the proxy-based reconstruction of\n2\natmospheric CO before and during the CPE (Foster et al. 2017); second, the\n2\nsimulated global mean surface temperatures are close to those previously\nreconstructed (Judd et al. 2024; Scotese et al. 2021). A similar approach was also\napplied in the previous studies to reconstruct the deep-time Earth’s climate (e.g., Li et\nal., 2022, 2023). It should be noted that the simulated climate change patterns due to\nthe greenhouse effect do not differ much depending on the CO level. Please see lines\n2\n436–446 of the revised manuscript (clean version).\nFoster, G. L., Royer, D. L., & Lunt, D. J. Future climate forcing potentially without\nprecedent in the last 420 million years. Nat. Commun. 8, 14845 (2017).\nJudd, E. J. et al. A 485-million-year history of Earth’s surface temperature. Science\n385, eadk3705 (2024).\nLi, X. et al. A high-resolution climate simulation dataset for the past 540 million\nyears. Sci. Data 9, 371 (2022).\nLi, X. et al. Climate variations in the past 250 million years and contributing factors.\nPaleoceanogr. Paleoclimatol. 38, e2022PA004503 (2023).\nScotese, C. R., Song, H., Mills, B. J. & van der Meer, D. G. Phanerozoic\npaleotemperatures: The earth’s changing climate during the last 540 million\nyears. Earth Sci. Rev. 215, 103503 (2021).\n[5] The analytical uncertainty of TOC and C and Hg isotope analyses are also\nmissing.\n[6] I understand that some coauthors are experts on Mesozoic and Cenozoic\nhyperthermals/climate changes. However, there are quite some mentions of Triassic-\nJurassic, Cretaceous OAEs, PETM, Oligo-Mio, and sometimes Carboniferous. These\n1\nbarely relate to this study (late Triassic) and, when appear so often, are distractions to\nthe central theme of this manuscript. Nevertheless, all these are fixable and should not\ntarnish the overall quality of this manuscript.\nReply: Thank you very much. We fully understand your concern regarding the\ninclusion of references to hyperthermals/climate events from other periods. The\nterminology used to describe hyperthermals, such as \"Pluvial Episode\", \"Extinction\nEvent\" and \"Oceanic Anoxic Event\", is to some extent historically contingent and\nmay obscure the underlying commonalities among these events. We think that these\ncomparisons serve to highlight the common features and underlying processes that\nlink the CPE to other well-documented climatic events. The similarities suggest these\nevents share a fundamental nature as hyperthermal episodes.\n[7] Line 32, “non-coldhouse climate” is not a very good term to me. Is non-coldhouse\nequal to warm house?\nReply: Thank you very much. We fully agree with you that “non-coldhouse climate”\nis not a good term. In order to clarify this issue, we changed the term “non-coldhouse”\nto “warmhouse”. Please see lines 32 and 271.\n[8] Line 35, not very clear what are the “eastern continents”. There was one continent\nat the time—the Pangea. I am not aware of any Carnian succession in either pole.\nReply: Thank you very much. We have revised the sentence to: \"The CPE\nhydrological cycle was typified by increased aridification in continental interiors and\nmultiple precipitation centres at low-latitude eastern regions of Pangea and at the\npoles.\" We would like to clarify that the polar records are indeed limited, and this\nresult is based on Earth system model simulations. Please see lines 33–35.\n[9] Line 47, the word “remarkable” should be avoided in scientific writing.\nReply: Thanks. We changed “remarkable” to “significant”. Please see line 47.\n4\n[10] Line 56 the words in brackets are redundant and probably not entirely accurate.\nWhat is left today as the Wrangellia LIP was only a fraction of its original size.\nReply: Thank you very much for pointing out this issue. We fully agree with you that\nour original description is redundant and not entirely accurate. We deleted “few\nbasalts were submarine; most were subaerial”. Please see line 55.\n[11] Lines 77-78 I would change to “the manifestation of global hydrological cycle\nchanges” ….\nReply: Thanks, done. Please see lines 77–78.\n[12] Lines 129-137 These are discussions rather than results. One might consider\nmoving these words to later chapters.\nReply: Thank you very much. Since we have chosen to combine the \"Results\"\nand \"Discussion\" sections in our paper, we believe that explaining the POE here provides\na more coherent flow. We hope this structure enhances the overall clarity and\nconnection of the ideas presented.\n[13] Lines 119-121 Rock Eval analysis is not described in the method.\nReply: Thank you. The core experimental methods were included in the main text,\nwhile the additional experiments (U-Pb dating, Rock Eval, compound-specific carbon\nisotopes and kerogen macerals analysis) are placed in the supplementary information\nto avoid overwhelming the maintext of the paper. In order to clarify this issue, we\nadded a citation in this text “analysis methods in Supplementary Text 4”. Please see\nline 148.\n[14] Lines 140-141 mis-citations of references\nReply: Thanks, corrected. Please see lines 168–169.\n[15] Line 147, not easy to follow here. of the CPE?\nReply: Thanks, corrected. Please see line 174.\n[16] Line 179, I would delete the example. Methane hydrates are too speculative for\nthe Carnian case and there is no evidence for it.\nReply: Thanks, done. We changed the sentence to “A precursor carbon release or\n5\nwarming event may signal the growing instability of thermally sensitive carbon\nsources, potentially triggering a positive feedback loop to sustain subsequent\nwarming”. Please see lines 203–205.\n[17] Lines 188-190, this is not an isolated case for the Carnian. As a matter of fact,\nmost carbon emission estimations from major LIPs do not match corresponding d13C\nexcursions.\nReply: Thank you very much, and we fully agree with you. At your suggestions, we\nadded a statement to acknowledge that this issue is not unique to the Carnian, as most\ncarbon emission estimations from major LIPs do not match the corresponding δ13C\nexcursions, as observed in events such as the Triassic-Jurassic transition and the\nPaleocene-Eocene Thermal Maximum. Please see lines 217–221.\n[18] Line 194 GMAT of 23-24 represents a significant warm interval. This sentence\nalso miscites literature. These estimated GMATs are compiled and should be used\nwith great caution if cited this way.\nReply: Thank you very much for pointing out this issue. We reconstructed the global\nair temperature and sea surface temperature separately in the simulation. Thus, we can\nverify the simulation output from two aspects: 1) comparing the modeling air\ntemperature with the compiled global average temperature (Scotese et al., 2021; Judd\net al., 2024). Although the estimated GMATs are compiled, these could initially\nconstrain the fundamental climate state. 2) We supplement the comparison of SST\nreconstruction of simulation and oxygen isotope records from conodont apatite from\neastern Tethys (South China) prior to the CPE (pCO set as 568 ppmv). Following\n2\nyour suggestions, we changed the sentence to “Palaeotemperature reconstructions\nsuggest relatively warm climatic conditions before the CPE, with a global mean air\ntemperature of ~23–24oC (Judd et al., 2024; Scotese et al., 2021) and tropical sea\nsurface temperatures in eastern Tethys of ~27℃ (Sun et al., 2016).” Please see lines\n221–224.\nJudd, E. J. et al. A 485-million-year history of Earth’s surface temperature. Science\n385, eadk3705 (2024).\nScotese, C. R., Song, H., Mills, B. J. & van der Meer, D. G. Phanerozoic\npaleotemperatures: The earth’s changing climate during the last 540 million\n6\nyears. Earth Sci. Rev. 215, 103503 (2021).\nSun, Y. D. et al. Climate warming, euxinia and carbon isotope perturbations during the\nCarnian (Triassic) crisis in South China. Earth Planet. Sci. Lett. 444, 88–100\n(2016).\n[19] Lines 194-195, ambiguous. Under what specific conditions do the authors refer\nto as? What is the GMAT that AWI-ESM gives in this study?\nReply: Thank you very much. The AWI-ESM simulated global mean surface\ntemperature under 568 ppmv is 23.35 oC. The simulated global mean surface\ntemperature heavily depends on the selected CO level, which is artificial. Therefore,\n2\nwe changed this sentence to “Under such warm conditions (Fig. 4a), the global\npermafrost surface area should be much smaller than that it is today (Biskaborn et al.,\n2019).” Please see lines 224–225.\nBiskaborn, B. K. et al. Permafrost is warming at a global scale. Nat. Commun. 10, 264\n(2019).\n[20] Lines 199-204, The argument is not convincing. Yes, the dissociation of marine\nmethane hydrates could account for the d13C excursion, but there is no evidence for\nsuch events. A decrease in d13C can be triggered in a few scenarios, e.g., a decrease in\nprimary productivity, less burial of organic carbon etc. What is the reason the methane\nhydrate scenario stands out in the Carnian case?\nReply: Thank you. We acknowledge that presently there is no direct evidence for\nmarine methane hydrate dissociation during the Carnian. While other processes, such\nas decreased primary productivity or less burial of organic carbon, can also cause a\nδ13C decrease, we would like to emphasize that we merely proposed a hypothesis. At\nthe very least, the total amount of methane that could have been released is sufficient\nto account for the magnitude of the CIE observed. Hopefully, other researchers will\nfind direct evidence for this hypothesis based on sedimentological or/and geochemical\nanalyses.\n[21] Lines 208-209 yes, this is a simple explanation but not necessarily represent the\nwhole picture.\nReply: Thank you very much for your valuable comment. We fully agree with you\n7\nthat the scenario is a simplified explanation and does not capture the full complexity\nof the event. While we propose the rapid release of isotopically depleted carbon from\nmethane hydrates as one possible mechanism, we acknowledge that other factors may\nhave played significant roles in shaping the CPE. Following your suggestion, we\nadded the statement: “However, we recognise that this is a simplified scenario, and\nthe complexity of the event likely reflects multiple contributing factors. Further\ninvestigation is needed to understand fully the interplay of various processes that\ncould have shaped the CPE”. Please see lines 238–241.\n[22] Line 226, I don’t follow the symbol “↑”.\nReply: Thanks, deleted. Please see line 255.\n[23] Lines 243-245, I couldn’t follow the argument here. What does “climate-carbon-\ncycle interaction” really mean here? Carbon cycle is always coupled with the global\nclimate.\nReply: Thank you very much. Climate and carbon cycle are profoundly coupled\nsystems, as the carbon-cycle processes covary with climate-related factors (e.g.\ntemperature, hydrological cycle, soil respiration, net primary productivity, CO\n2\nsolubility, weathering). For the carbon cycle-climate feedback system, the carbon\ncycle controls the concentrations of key greenhouse gases (CO and CH ) in the\n2 4\natmosphere, thereby modulating Earth's global temperature. Furthermore, the cycle-\nclimate feedback could be paced by the orbital forcing (e.g. for the last 6 Myr,\nspanning from the earliest Pliocene to present, during eccentricity minima, cooler and\nmore stable climates, within a generally warm background, facilitated the expansion\nof continental carbon reservoirs, leading to greater land storage of isotopically light\ncarbon and a corresponding rise in marine dissolved inorganic carbon (δ¹³C-DIC),\nwith the reverse occurring during maxima). Therefore, based on the proposed orbital\nforcing of climate-carbon-cycle interaction in Cenozoic (De Vleeschouwer et al.,\n2020), we refer to the feedback system including carbon cycle and climate changes as\n‘climate-carbon-cycle interaction’.\nDe Vleeschouwer, D. et al. High-latitude biomes and rock weathering mediate\nclimate–carbon cycle feedbacks on eccentricity timescales. Nat. Commun. 11,\n5013 (2020)\n8\n[24] Lines 245-247, My apologies for not following the argument here. The sentence\nis grammatically incorrect to me. What does the “last 6 Myr” refer to? and how does\nthe Carboniferous example relate to this study (late Triassic)?\nReply: Thank you very much. We refer here to the last 6 Myr, spanning from the\nearliest Pliocene to present, which is typical of unique coldhouse climate–carbon\ncycle dynamics. In order to avoid the confusion, we rephrased this sentence as:\n“Therefore, this climate–carbon interaction may be the norm after the emergence of\nvascular plants, whereas the coldhouse climate–carbon cycle dynamics of the earliest\nPliocene may represent a more unusual situation.” Please see lines 275–278.\n[25] Lines 255-257, this lengthy part can be revised to “Our AWI-ESM simulations\nconfirms a ….\nReply: Thanks. We changed the sentence to “Our AWI-ESM simulations confirm a\nmore arid and warmer climate during this interval in the Junggar Basin”. Please see\nlines 285–286.\n[26] Line 262 “poleward shift of precipitation patterns” is not a proper description and\nit’s hard to guess what the authors mean.\nReply: Thank you very much. We here refer to the poleward shift of pre-existing\nprecipitation zones. The poleward shift of existing climatic/precipitation zones driven\nby rising global temperatures has generally occurred during the warm periods of\ngeological history (e.g. Pliocene warmth, Abell et al., 2021). In order to avoid the\nconfusion, we rephrased this sentence: “Our results show that precipitation changes\nduring the CPE exhibited spatial heterogeneity, accompanied by a poleward shift of\npre-existing precipitation zones and no evidence of global humidification”. Please see\nlines 287–289.\nAbell, J. T., Winckler, G., Anderson, R. F., & Herbert, T. D. Poleward and weakened\nwesterlies during Pliocene warmth. Nature, 589, 70–75 (2021).\n[27] Line 263 reword this sentence. Mountains can block moisture transport.\nReply: Thanks, done. We revised the sentence to “Moreover, mountains and extensive\ncontinental areas can block moisture transport, resulting in enhanced net evaporation\n9\nwithin the interior of supercontinents (Pangaea)”. Please see lines 292–294.\n[28] Lines 258-281 This paragraph could be improved after a proper rewrite.\nReply: Thank you very much. We rephrased this paragraph. Please see lines 287–312:\n“Our results show that precipitation changes during the CPE exhibited spatial\nheterogeneity, accompanied by a poleward shift of pre-existing precipitation zones\nand no evidence for global humidification. The heterogeneous pattern of precipitation\nchanges is characterized by predominantly increased precipitation near the Equator\nand at high latitudes, while subtropical latitudes exhibit diminished rainfall (Fig. 4b).\nMoreover, mountains and extensive continental areas can block moisture transport,\nresulting in enhanced net evaporation within the interior of supercontinents\n(Pangaea)47. In contrast to previous hypotheses regarding unusual global\nhumidification during the CPE 2,7,13,26, the integrated stratigraphy and Earth system\nmodel highlight the spatial variations in global precipitation patterns, characterized by\nincreased aridification in continental interiors and the emergence of multiple\nprecipitation centres in low-latitude eastern continents and polar regions, including\nthe Arctic, northeastern Tethys, northeastern Gondwana, and the Antarctic (Fig. 4b).\nThese precipitation changes are corroborated by geological records throughout the\nCPE (e.g. the progradation of the largest delta system in geological history in the\nBoreal Ocean and the westward migration of its main depocenter66; the large-scale\nincrease of terrigenous inputs and the extinction of carbonate platforms in the\nsouthwestern Tethys continental shelf67,68 and South China11,69) (Fig. 1). Our\nmodelling of annual global changes, consistent with other palaeoclimatic\nsimulations32,70,71, is unable to replicate the wetter climate in the western and\nnorthwestern Tethys as indicated by previous sedimentological evidence (e.g., ref.3,51).\nThe remaining proxy–model differences may be due to unresolved local features in\nprecipitation or the implementation of palaeotopography. Nevertheless, the newly\nproposed pattern appears to largely conform to established hydroclimate features\nobserved in other past warm periods72, thereby amplifying the spatial heterogeneity in\nprecipitation distribution.”\n[29] Lines 295-297 Colleagues working on modern climate change won’t be fond of\nsuch a statement.\nReply: Thank you very much. At your suggestion, we deleted this statement, which\n10\ndoes not influence the paper.\n[30] Line 542 what is a Retsch RS200? I guess it is a rock saw.\nReply: Thanks. Retsch RS200 is a machine for sample crush. We revised the sentence\nto “Samples were trimmed to remove visible veins and weathered surfaces and ground\nusing a sample crush (Vibratory Disc Mill RS 200)”. Please see lines 332–333.\n[31] Line 554 in per mille (‰) relative to ……\nReply: Thanks, corrected. Please see line 342.\n[32] Line 557 Reproducibility and repeatability of\nReply: Thanks, added. Please see lines 345–348: “The analytical uncertainty for TOC\nwas calculated as a relative error of less than ± 5%, and the standard deviation for\nδ13C was ± 0.2‰ (1σ), both determined through replicate analyses of standard\norg\nsamples.”\n[33] Line 582 delete units of\nReply: Thanks, deleted. Please see line 372.\n[34] Line 587 There is no mention of the reproducibility of Hg isotopes.\nReply: Thanks, added. Please see line 379: “Reproducibility of Δ199Hg was better than\n± 0.05‰ (2σ).”\n[35] Line 612 “the” change to a\nReply: Thanks, done. Please see line 402.\n[36] Line 651, I don’t follow the statement here. Solar luminosity and ice coverage of\nthe Carnian world (ice-free) should differ significantly from the pre-industry world\n(iced world). Revise to clarify this unambiguity.\nReply: Thank you very much. We fully agree with you that the solar constant should\nbe different from today. However, this will not affect the model results on the\nsimulated climate changes induced by CO . In our simulations, the Earth’s orbit and\n2\nsolar constant are kept the same as present-day. While there is no continental ice\n11\nsheet. We added detailed explanation in the revision: “There is no continental ice\nsheet”. Please see lines 433–434.\n[37] Lines 655, 658 I don’t follow the term “quasi-equilibrium”, i.e., the simulations\ndid not reach equilibrium?\nReply: Thank you very much for pointing out this issue. Strictly speaking, without\n6000 years simulation, the deep ocean cannot reach an equilibrium state (Li et al.\n2013). However, 1000 years is enough for the model to reach a surface equilibrium\nstate, which is sufficient for us to examine the climate change on the precipitation\npattern. In order to clarify this issue, we have revised the text from “quasi-\nequilibrium” to “surface equilibrium”. Please see lines 449–452: “The 568 ppmv\nexperiment was run for 2000 years to allow the climate system to reach a surface\nequilibrium state. The 1704 ppmv experiment, initialized from the first experiment,\nwas run for 1000 years. This procedure allows the upper ocean and surface climate to\nachieve an equilibrium state.”\nLi et al. Deep-ocean heat uptake and equilibrium climate response. Clim. Dyn. 40,\n1071–1086 (2013).\n[38] Line 657, 1000 model year is really low. Did the simulation collapse?\nReply: Thanks. For the surface climate, 1000 years are enough to reach an\nequilibrium state, which is usually quantified as a surface temperature trend being less\nthan 0.1 degrees/century. The initial state of Triassic simulation is very difficult to\nobtain, with many times collapses. However, after 10 years simulation, the model\nworks fine. In order to clarify this issue, we added detailed explanation in the\nrevision. Please see comment 37.\n[39] Fig. 2 the black shaded parts in the log stand for black shales, do they? I didn’t\nsee any black shale in the field photo (Fig. S1). Maybe include some better field\nphotos. There are both extended data figures and supplementary figures (in the\nsupplementary materials). The two systems are not very easy to follow.\nReply: Thank you very much. At your suggestion, we added additional field photos in\nFig. S1. We have now moved all extended data figures to the supplementary\ninformation section and updated the figure numbers accordingly.\n12\n[40] Extended Data Fig. 3 The Tibetan record is very poor, and is not a good case to\ncorrelate. Ref 30 gave a d13Carb value lower than -5 per mille and down to almost -\n10 per mille. This cannot be true for any normal marine carbonate. The numbers\nmight have measured from carbonate cements in sandstone or diagenetically highly\naltered carbonates.\nReply: Thanks. We fully agree with you that the Tibetan record is quite poor. We\ndeleted the Tibetan record. Please see the Fig. S16.\n[41] Text S2-strangely, the U-Pb dating was not included in the Method but in the\nsupplementary.\nReply: Thank you very much. The core experimental methods are already included in\nthe main text, while the additional experiments (U-Pb dating, Rock Eval, compound-\nspecific carbon isotopes, and kerogen macerals analysis) are primarily supportive and\nprovide supplementary data. As such, we have placed them in the supplementary\ninformation to avoid overwhelming the maintext of the paper.\n[42] Fig. S8 (and other log figures) Mud/Sha is better to spell in full.\nReply: Thank you very much. We added the full explanations of the abbreviations in\nthe figure captions for Fig. 2, Fig. S9, Fig. S11 and Fig. S15.\n[43] Text S4 Compound-specific carbon isotopes are not mentioned in the main text.\nReply: Thank you very much. The compound-specific carbon isotopes data support\nour interpretation that the bulk organic carbon-isotope record from the Dalongkou\nsection dominantly reflects the atmospheric δ13C-CO signal, which in turn indicates\n2\nglobal carbon-cycle perturbations. We have mentioned this in lines 146–150.\nHowever, given that the results are not directly relevant to the main discussion, we\nhave included them in Text S4 instead.\nReviewer 2:\nThe manuscript by Zhao et al. provides a new record of the CPE from the lacustrine\nJunggar Basin in northwestern China. This manuscript presents multiple data,\nincluding magnetic susceptibility, U-Pb age, C and Hg isotopes, elemental\ngeochemistry, and palynological data, combined with Earth System modelling, to\n13\ndiscuss potential driving mechanisms for the CPE, and coeval changes to the\nhydrological cycle. Overall, the methods are appropriate and the data are valuable.\nHowever, some important issues need to be addressed before it can be considered. My\nmain suggestions are the following:\nReply: We are grateful to you for your positive and encouraging comments. Please\nsee the responses below.\n[44] Due to the lack of volcanic rocks in the study strata, the authors only determine\nthe age using tuffaceous sandstone. The authors need more description how did your\nresearch identify Carnian Pluvial Episode? The CPE does not only mean carbon\nisotope excursion.\nReply: Thank you very much. We fully agree with you that the CPE does not only\nmean a carbon isotope excursion. In the original description, the Carnian Pluvial\nEpisode (CPE) onset corresponds with an initial pulse of siliciclastic material and the\nshift of the carbonate factory from predominantly microbial reefs to metazoan-\ndominated reefs (e.g., Dal Corso et al., 2020). However, this lithofacies change cannot\nbe used in some other marine and continental deposits (e.g., marine carbonate, deep-\nsea bedded chert, lacustrine mudstone). Based on the U-Pb geochronology and\nbiostratigraphic results, the carbon isotope excursion can provide an additional\nconstrain on the onset of the CPE (Dal Corso et al., 2015), especially for lacustrine\ndeposits that lack the marine biozones (e.g., Lu et al., 2021). In our study, we\ncombined biostratigraphy (palynology and vertebrate fossils; Peng et al., 2024) and\nU-Pb dating to place the CPE (234–232 Ma) in the lower part of the Huangshanjie\nFormation, and further constrained the onset of the CPE using carbon isotope data. In\nconclusion, we identified the CPE based on the combination of U-Pb geochronology,\nbiostratigraphy, and carbon-isotope stratigraphical evidence, thereby avoiding the\nuncertainty inherent in interpreting data from a single proxy. To clarify this point\nfurther, we added the following sentence in the revised manuscript: “We combined\nbiostratigraphy (palynology and vertebrate fossils) and U-Pb dating to place the CPE\nin the lower part of the Huangshanjie Formation, and further constrained the onset of\nthe CPE using carbon isotope data.” Please see lines 141–143.\nDal Corso, J. et al. Carbon isotope records reveal synchronicity between carbon cycle\nperturbation and the “Carnian Pluvial Event” in the Tethys realm (Late Triassic).\nDal Corso, J. et al. Extinction and dawn of the modern world in the Carnian (Late\nTriassic). Sci. Adv. 6, eaba0099 (2020).\nLu, J. et al. Volcanically driven lacustrine ecosystem changes during the Carnian\nPluvial Episode (Late Triassic). Proc. Natl. Acad. Sci. U.S.A. 118, e2109895118\n(2021).\nPeng, J. et al. Floral and faunal biostratigraphy of the Middle–Upper Triassic\nKaramay and Huangshanjie formations from the southern Junggar Basin, China.\nGeol. Soc. Spec. Publ. 538, 41–66 (2024).\n[45] Please provide more discussions concerning spores and pollen in the manuscript.\nHow to evaluate the contribution of eolian activity on palynological compositions? If\nthe eolian activity is strong, the spores and pollen could be derived from other distant\nregions (not surrounding regions). Please clarify it. Besides, I strongly suggest that the\nauthors add climate status in Extended Data Fig. 2. Since the authors have measured\nelemental content, I strongly suggest that they use geochemical proxies (e.g., CIA) to\nreconstruct climate evolution in the study area.\nReply: Thank you very much. Traverse (2007) evaluates the contribution of eolian\nactivity to palynological compositions, noting that while pollen is small, low in\nspecific gravity, and suited for air transport, 95% of airborne pollen typically settles\nwithin a kilometer of the source plant (p. 503). Even when airborne pollen travels\nfarther, they are largely overwhelmed by those transported by water (p. 507). As such,\nairborne pollen makes up a tiny component of local palynofloras and are rarely\ndetected in sediments. In our study, due to the restricted nature of the inland Junggar\nBasin, the palynological data are primarily derived from pollen and spores transported\nby water, making them well-suited for reconstructing the region’s palaeovegetation.\nTherefore, we suggest that eolian activity has minimal impact on our data and\ninterpretations. In revision, we add some discussions: “As suggested by Traverse\n(2007), most pollen and spores are transported by water, with airborne pollen being a\nminor component and primarily derived from nearby regions rather than distant areas.\nFurthermore, since the Junggar Basin was a highly restricted basin, aeolian activity is\nlikely to have had a minimal impact on the palynological compositions. Therefore,\nour palynological data are well-suited for reconstructing the palaeoclimate of the\nJunggar Basin”. Please see lines 402–408 in the supplementary information.\nas an indicator of variations in aridity and humidity in the climate. Please see the Fig.\nS15.\nWe have previously analysed the CIA index of the Huangshanjie Formation.\nUnfortunately, the index of compositional variability (ICV) shows that the\nHuangshanjie Formation in the Dalongkou section has experienced multiple\nweathering cycles. Therefore, the CIA is not applicable in the Dalongkou section.\nTraverse, A. 2007. Paleopalynology. Dordrecht, Springer.\n[46] Lines 122-126: The studied section displayed a CIE with an amplitude of 6.5‰,\nwhich is larger than coeval sedimentary successions (lines 52-54). Lines 202-204: the\nauthors suggest that the isotopically light carbon released during CIE1 may have\nmainly originated from dissociation of sub-ocean-floor methane hydrates. If it is true,\nboth marine and lacustrine should exhibit a similar amplitude of carbon isotope\nexcursion. Please clarify it.\nReply: Thank you very much. The carbon isotope curves from the sediments of the\nCPE indicate that the magnitude of each negative carbon isotope excursion can vary\nsignificantly depending on the geological context (Dal Corso et al., 2018). The δ13C\nvalues of both terrestrial and marine organic carbon are influenced by various factors,\nincluding the source of the carbon during photosynthesis by primary producers, the\ntype of photosynthetic pathway employed, and the environmental conditions at the\ntime (Diefendorf et al., 2010; Dal Corso et al., 2017, 2018). Additionally, in other\nglobal warming events, such as the Paleocene-Eocene Thermal Maximum (PETM),\nthe magnitude of the negative organic carbon isotope excursions varies across\ndifferent geological records (e.g., North Sea and Svalbard cores), even though the\nrelease of methane has also been implicated in driving the carbon isotope negative\nexcursion during this event (Kender et al., 2021).\nDal Corso, J. et al. Evaluating the use of amber in palaeoatmospheric reconstructions:\nthe carbon-isotope variability of modern and Cretaceous conifer resins. Geochim.\nCosmochim. Acta 199, 351–369 (2017).\nDal Corso, J. et al. Multiple negative carbon-isotope excursions during the Carnian\nPluvial Episode (Late Triassic). Earth Sci. Rev. 185, 732–750 (2018).\nthe studies of past and future climate. Proc. Nat. Acad. Sci. U. S. A. 107, 5738–\n5743 (2010).\nKender, S. et al. Paleocene/Eocene carbon feedbacks triggered by volcanic activity.\nNat. Commun. 12, 5186 (2021).\n[47] Lines 126-129: It is recommended to define the CPE onset because CPE is\nCarnian Humid Episode, but not only carbon isotope excursion.\nReply: Thank you for your suggestion. Although the CPE is defined by increased\nhumidity, its climatic changes exhibit significant spatial variability, making a purely\nclimate-based definition unsuitable. Indeed, many regions did not experience a\nmarked increase in humidity (Figs. 1 and 4 in the maintext). We fully agree with you\nthat the CPE can not be solely defined by the carbon isotope excursions. In our study,\nwe identified the CPE based on the combination of U-Pb geochronology,\nbiostratigraphy, and carbon-isotope stratigraphical evidence, thereby avoiding the\nuncertainty inherent in interpreting data from a single proxy. Based on previous CPE\nrecords, the CIE1 is considered to coincide with climate change and biological\nturnover, making it a globally significant marker for the onset of the CPE (e.g., Dal\nCorso et al., 2012, 2015, 2018, 2020; Lu et al., 2021; Miller et al., 2017; Sun et al.,\n2016). Therefore, we have used the CIE1, rather than POE, as the onset of the CPE. A\nsimilar approach has been used for defining other major events, such as OAE 1a, with\ncarbon isotope excursions serving as global markers even in the absence of black\nshales, as seen in marine records from the Mid-Pacific Mountains (Ando et al., 2008)\nand terrestrial records from northwestern China (Sun et al., 2024).\nAndo, A., Kaiho, K., Kawahata, H., Kakegawa, T. Timing and magnitude of early\nAptian extreme warming: Unraveling primary δ18O variation in indurated pelagic\ncarbonates at Deep Sea Drilling Project Site 463, central Pacific Ocean.\nPalaeogeogr. Palaeoclimatol. Palaeoecol. 260, 463–476 (2008).\nDal Corso, J. et al. Discovery of a major negative 13C spike in the Carnian (Late\nTriassic) linked to the eruption of Wrangellia flood basalts. Geology 40, 79–82\n(2012)\nDal Corso, J. et al. Extinction and dawn of the modern world in the Carnian (Late\nDal Corso, J. et al. Multiple negative carbon-isotope excursions during the Carnian\nPluvial Episode (Late Triassic). Earth Sci. Rev. 185, 732–750 (2018).\nDal Corso, J. et al. Carbon isotope records reveal synchronicity between carbon cycle\nperturbation and the “Carnian Pluvial Event” in the Tethys realm (Late Triassic).\nGlobal Planet. Change 127, 79–90 (2015).\nLu, J. et al. Volcanically driven lacustrine ecosystem changes during the Carnian\nPluvial Episode (Late Triassic). Proc. Natl. Acad. Sci. U.S.A. 118, e2109895118\n(2021).\nMiller, C. S. et al. Astronomical age constraints and extinction mechanisms of the\nLate Triassic Carnian crisis. Sci. Rep. 7, 2557 (2017).\nSun, Y. D. et al. Climate warming, euxinia and carbon isotope perturbations during the\nCarnian (Triassic) crisis in South China. Earth Planet. Sci. Lett. 444, 88–100\n(2016).\nSun, F. et al. Methane fueled lake pelagic food webs in a Cretaceous greenhouse\nworld. Proc. Natl. Acad. Sci. U.S.A. 121, e2411413121 (2024).\n[48] Lines 124, 127 and 138: The paper is astronomically tuned based on the long\neccentricity cycle (405 kyr). However, the time intervals of CIE1, CIEs, and POE\ndiscussed in the text are significantly shorter than 405 kyr, such as \"139.2 kyr,\" \"19\nkyr,\" and \"374.2 kyr.\" This may lead to unreliable results for these age data. It is\nsuggested that the authors employ certain methods to minimize errors or discuss and\npresent the magnitude of the errors.\nReply: Thank you very much. Firstly, the high- resolution sedimentological and\npetrographic evidence has indicated no remarkable unconformity within the\nHuangshanjie Formation. Then, we presented two tuning schemes based 405-kyr long\neccentricity cycle and 173-kyr obliquity cycle, revealing highly correlated\nastronomical signals corresponding to the 405-kyr long eccentricity, 173-kyr\nobliquity, and 131–95-kyr short eccentricity components. The two tuning schemes\nconstrain the CPE interval within basically consistent temporal range. This\ndemonstrates the continuity of our strata on the 105-year scale. Because the obliquity\nand precession terms are not stable through geological history and susceptible to\nsedimentary noise, there is currently no reliable method to evaluate the error of\nastrochronology on 104-year scale and smaller scales. The recent classical\n18\ncyclostratigraphic studies are also limited by this problem and widely accepted the\n405-kyr tuned timeframe. We interpolate and estimate the duration using the average\nsedimentation rate within a 405-kyr cycle.\n[49] Lines 82-84: The author stated that they provided high-resolution\npalaeontological, sedimentological and geochemical data from the Dalongkou section\nto reconstruct of the structure of the CPE onset. However, detailed sedimentological\ndescription is completely missing in the manuscript. Additionally, the coordinate of\nthe studied section needs to be added in the Geological setting.\nReply: Thank you for your comment. All the sedimentological descriptions have been\nprovided in Supplementary Data 2. Additionally, we have added the coordinates of the\nstudied section to the Geological Setting section. Please see line 96.\n[50] Line 140: The study of the Bagong Formation on the Qinghai-Tibet Plateau\nshould be 30 of your references; Rather than 23, 23's study was a cyclostratigraphy\nstudy conducted by Miller et al., 2017 on a well in the UK;\nReply: Thanks, corrected.\n[51] Lines 154-456: It seems that elevated Hg occurred before the CPE onset\n(Extended Data Fig. 2). Besides, the vertical variation of δ13C and Hg/TOC in Fig 3\norg\nand Extended Data Fig. 2 is different, please unify it.\nReply: Thanks. Sure, elevated Hg occurred before the CPE onset (CIE 1),\ncorresponding to the POE. Due to the limitations of the Extended Data Fig. 2, which\nshows data spanning 316.20 m, it is difficult to clearly discern the relationship\nbetween POE and Hg/TOC. Therefore, in the Fig. 3, we have zoomed in on the region\nat the onset of the CPE, which is the main focus of this study. The data in Extended\nData Fig. 2 and Fig. 3 are consistent.\n[52] Line 541: provides detection limits and accuracy of δ13C and TOC;\norg\nReply: Thanks, added. Please see lines 345–348.\n[53] Line 568: Detection limit and accuracy of mercury isotope\nReply: Thanks, added. Please see line 379.\n19\n[54] Fig. S1: Please exhibit clearer filed photos in Fig. S1b and c. Besides, it is\nrecommended to add the micrograph of tuffaceous sandstone.\nReply: Thank you very much for your suggestion. We added clearer filed photos in\nthe Fig. S1. Our previously collected dating samples have all been used up, and we\nrecently flew back to Xinjiang to collect new samples. We conducted a series of thin\nsection analyses on these fresh samples and identified the presence of tuffaceous\nmaterial, although in very low amounts, please see Fig. S1. After discussions with our\npetrological colleagues, we have revised the classification to sandstone, ensuring that\nthe terminology is both accurate and rigorous.\nTherefore, the ages we analyzed provide the maximum depositional ages for the\nstudied strata and serve as supplementary evidence for the palynological and carbon\nisotope stratigraphy. We added some discussions in the supplementary information:\n“According to the “law of detrital zircon”, the deposition of the strata in question\ncannot not be older than the age calculated from the youngest zircon grains from the\nyoungest magmatic events33–36. Therefore, the maximum depositional age (MDE) can\nbe close to the real depositional age, especially when the former is consistent with the\nbiostratigraphical age37–40. In this study, the youngest zircons are morphologically\nuniform with no visible signs of rounding due to even minor sedimentary abrasion\nduring transportation, a conclusion also supported by the angular shapes of quartz\ngrains (Fig. S1f, g). These observations indicate that the depocenter of two sandstone\nsamples from the Dalongkou section was situated near the magmatic source of the\nzircons. Considering that the maximum depositional ages of two samples are\nconsistent with the age analyzed from the sporo-pollens, we use the maximum\ndepositional ages to tightly constrain the age of the CPE in this study.”\nThe vertebrate Fukangichthys fauna and the palynological zonation (Aratrisporites,\nDictyophyllidites-Aratrisporites, and Lycopodiacidites-Stereisporites) suggest that the\nboundary between the Middle Triassic and Upper Triassic lies between the uppermost\nKaramay Formation and the bottom of the Huangshanjie Formation (Peng et al.,\n2022). The U-Pb radioisotopic dating on two sandstone samples from the uppermost\nKaramay and lower Huangshanjie layers shows a maximum depositional age of 234.8\n± 0.8 Ma to 232.9 ± 0.7 Ma (Fig. 2, Supplementary Text 2), further constraining the\nlower Huangshanjie Formation to the lower–middle Carnian. This places the CPE\n(234–232 Ma) in the lower Huangshanjie Formation (between the lowest layer and the\nstratigraphic level of the sample with the youngest depositional age of 232 Ma). The\nWe have revised the petrological description, please see lines 109–116.\n[55] Extended Data Fig. 3: The red dashed line (the onset of Volcanism) is placed\nbefore the rise in Hg/TOC, but the data for Central Japan seems not to align with this.\nSo, some adjustments may be needed.\nReply: Thank you very much. We have made the adjustments. Please see Fig. S16.\n[56] Although the English text is understandable, it can and should be improved to\nmeet the journal's standard.\nReply: Thank you very much. We invited two native English speakers (our co-authors\nHugh C. Jenkyns and Philippe Claeys) to proofread our text.\nReviewer 3:\n[57] In this manuscript, Zhao et al. investigate the Carnian Pluvial Episode (CPE), a\nmajor climate change that occurred around 234 to 232 million years (Ma) ago. The\nstudy examines climate and carbon-cycle dynamics during the CPE using high-\nresolution multi-proxy data from a lacustrine succession in the Junggar Basin,\nnorthwestern China. The findings highlight the rapid onset of the CPE, potentially\ndriven by volcanism and carbon-cycle feedbacks, as well as the in-phase relationship\nbetween terrestrial carbon cycling and orbital eccentricity. Changes in precipitation\npatterns across different latitudes are also discussed, highlighting the spatial\ncomplexity of the CPE and its diverse regional impacts.\nThe topic developed in the manuscript is of interest to the international scientific\ncommunity, contributing to research on the CPE and its links to other warm events in\nEarth's history. While the study provides important insights into global climate–\ncarbon-cycle interactions and the heterogeneous nature of the CPE, some aspects of\nits findings align with recent studies (e.g., Dal Corso et al., 2024; Zhang et al., 2024),\nmaking its novelty appear limited. Nonetheless, this study addresses gaps in the\nterrestrial record of CPE, where dating limitations often restrict detailed links to the\nCPE. Also, its multidisciplinary approach and focus on mechanisms driving the CPE's\nrapid onset offer valuable insights into this poorly understood climatic event.\nHowever, the text is wordy in some parts, contains several typos, and needs major\nrevisions (rephrasing and rewriting) for clarity and presentation. I have provided a list\n21\nof comments and suggestions, organised by line number, that the authors should\naddress.\nReply: We are grateful for the positive and encouraging comments. Please see the\nresponses below.\n[59] Line 46: Please cite the recent article by Lin et al. (2025)\n(DOI: https://doi.org/10.1016/j.marpetgeo.2025.107289) on deoxygenation preceding\nthe CPE in the Qiangtang Basin. The findings on the environmental,\npaleoceanographic, and organic matter controlling processes preceding the CPE and\nthe role of sedimentary organic matter in the global carbon cycle are relevant to your\nwork and could be included in your discussion.\nReply: Thanks, done. Please see lines 45–47.\n[60] Line 48: Please fix the typo: 'phenomana' to 'phenomena'\nReply: Thanks, done. Please see line 48.\n[61] Line 55-59: The sentence could be rephrased for better clarity and flow. For\nexample:' The emplacement of the Wrangellia Large Igneous Province (LIP) is\nconsidered a primary trigger of the CPE, likely amplified by the release of isotopically\nlight CO₂ from surface feedbacks into the ocean-atmosphere system, driving a\nwarmer, more humid climate and associated negative CIEs.'\nReply: Thanks, done. Please see lines 55–58.\n[62] Line 70: Please include the CPE record from the Miankuhi Formation, Turan\nPlate (NE Iran) based on Mazaheri-Johari et al. (2021, 2022) in both Text S1 and Fig.\n1. Also, add the following references to the reference section:\n- Mazaheri-Johari et al. (2021), DOI: https://dx.doi.org/10.13130/2039-4942/15646\n- Mazaheri-Johari et al. (2022), DOI: https://doi.org/10.1016/j.palaeo.2021.110777\nReply: Thanks, done. Please see lines 20–21 in the Supplementary Information.\n[63] Line 70-72: I recommend refining the sentence for clarity, for example:\n'However, given the lack of high-resolution chronostratigraphic framework, the\ncorrelation between enhanced humidity on land and the CPE interval remains unclear.'\nReply: Thanks, done. Please see lines 69–71.\n22\n[64] Line 72-74: The sentence has a convoluted structure. I suggest rewriting it,\nfor example:' In several regions, including the basins of the Newark Supergroup in the\nUSA, sedimentary evidence of increased humidity during the CPE has not been\nidentified.'\nReply: Thanks, done. Please see lines 71–73.\n[65] Line 81: The reference to 'Supplementary Text 2' in the sentence could lead to\nconfusion as it could be interpreted as covering both biostratigraphy and radiometric\nage information. Since it focuses on U-Pb dating methodology, I suggest rephrasing it\nto 'radiometric methods in Supplementary Text 2' for clarity.\nReply: Thanks, done. Please see lines 79–83: “In this study, we report on a continuous\nlacustrine sequence (Dalongkou section) in the southern Junggar Basin, northwestern\nChina, which provides a record of the CPE based on biostratigraphy and radiometric\nages (radiometric methods in Supplementary Text 2) and allowed the construction of\nan integrated astronomically calibrated age model.”\n[66] Line 82: This sentence is wordy and needs rephrasing, for example: ‘The high-\nresolution palaeontological, sedimentological, and geochemical signals from the\nDalongkou section enable the detection of the CPE onset.’\nReply: Thanks, done. Please see lines 83–85.\n[67] Line 90: Add a comma after the word 'together'\nReply: Thanks, done. Please see line 90.\n[68] Line 102: The sedimentary wavelengths mentioned in the main text ('11 to 8 m')\ndiffer slightly from those in Supplementary Text 3 ('10.8 to 9 m'). Although the use of\n'ca.' allows some flexibility, it would be better to justify these differences to ensure\nconsistency and avoid confusion.\nReply: Thank you very much for pointing out this issue. Due to sedimentation rate\nchanges, specific orbital frequency bands may correspond to spectral peak clusters\ncomposed of distinct depth wavelengths. Thus, we use the high-confidence level\nspectral peaks corresponding to the wavelengths of ~10.8 m and ~9 m for calculation\nin the Supplementary Text 3. In the main text, we use a large range of the spectral\n23\npeak clusters associated with short eccentricity. We corrected the sedimentary\nwavelengths in the main text to 10.8 to 9 m to ensure the consistency with the\nSupplementary Text. Please see lines 124–131: “The spectral analysis of the MS\nseries indicates a series of obvious sedimentary wavelengths, i.e., ca. 34 m, 13.3 m,\n10.8 m, 9 m, 8 m, 3 m and 1.6 to 1.3 m (Supplementary Text 3), approximately in\naccord with the ratios of the 405-kyr long-eccentricity, 173-kyr obliquity, 125–95-kyr\nshort-eccentricity, ~33-kyr obliquity and ~21–17-kyr precession cycles around 234\nMa, based on the La2004 astronomical solution.”\n[69] Line 110: The phrase 'high quality of our astronomical calibration' is somewhat\nsubjective. It would be more appropriate to describe the calibration in terms of its\nreliability and precision. Please consider rephrasing it.\nReply: Thank you. We rephrased this sentence as 'The spectral analysis of the two\ntuning schemes shows highly correlated astronomical signals corresponding to the\n405-kyr long eccentricity, 173-kyr obliquity, and 131–95-kyr short eccentricity\ncomponents, thereby confirming the reliability of the astronomical calibration'. Please\nsee lines 135–138.\n[70] Line 110: 'shows' instead of 'show'\nReply: Thanks, done. Please see line 135.\n[71] Line 127: Please fix the typo: 'stratigrapically' to 'stratigraphically'\nReply: Thanks, done. Please see line 155.\n[72] Line 141: Please consider rephrasing, for example: 'However, the entire CPE\nwith episodic CIEs is generally considered to have lasted longer than 1 Myr based on\ncyclostratigraphy (~1.1 Myr), biostratigraphy and magnetostratigraphy (1.6 to 1.7\nMyr).\nReply: Thanks, done. Please see lines 169–171.\n[73] Line 171: Please fix the typo: 'redcution' to 'reduction'\nReply: Thanks, done. Please see line 197.\n[74] Line 176-180: Please consider rephrasing, for example: 'A precursor carbon\n24\nrelease or warming event may signal the growing instability of thermally sensitive\ncarbon sources, such as sub-ocean-floor methane hydrates, potentially triggering a\npositive feedback loop to sustain subsequent warming.'\nReply: Thanks, done. Please see lines 203–205: “A precursor carbon release or\nwarming event may signal the growing instability of thermally sensitive carbon\nsources, potentially triggering a positive feedback loop to sustain subsequent warming\n(Fig. 3).”\n[75] Line 194: Please add 'a' before 'global mean'\nReply: Thanks, done. Please see line 222.\n[76] Line 203: Please add 'the' before 'dissociation'\nReply: Thanks, done. Please see line 231.\n[77] Line 210: Change the punctuation: 'i.e.' to 'i.e.,'\nReply: Thanks, done. Please see line 237.\n[78] Line 211: Please add 'the' before 'Earth system'\nReply: Thanks, done. Please see line 238.\n[79] Line 211: Eliminate the preposition 'to' before 'the CPE'\nReply: Thanks, done. Please see line 238.\n[80] Line 215-218: Please consider rephrasing, for example: 'The orbitally driven\nchanges in Earth's hydrological processes and carbon cycles, occurring over tens of\nthousands to millions of years, form the underlying pattern of climate-carbon cycle\ninteractions.'\nReply: Thanks, done. Please see lines 245–247: “The orbitally driven changes in\nEarth's hydrological processes and carbon cycles, occurring over tens of thousands to\nmillions of years, form the underlying pattern of climate-carbon-cycle interactions.”\n[81] Line 218-222: The sentence needs to be rephrased for better readability.\nReply: Thanks, we revised the sentence to “Previous research has indicated that the\nclimate–carbon-cycle interaction was paced by 405-kyr long-eccentricity rhythm\n25\nthroughout the Oligo–Miocene, time interval followed by a striking phase reversal at\ncoldhouse conditions.” Please see lines 248–251.\n[82] Line 219: Please fix the typo: 'rhtthm' to 'rhythm'\nReply: Thanks, done. Please see line 249.\n[83] Line 222-226: Please break down the sentence and consider re-phrasing, for\nexample: 'During eccentricity minima, cooler and more stable climates, within a\ngenerally warm background, facilitated the expansion of continental carbon\nreservoirs. This led to greater land storage of isotopically light carbon and a\ncorresponding rise in marine dissolved inorganic carbon (δ¹³C-DIC), with the reverse\noccurring during maxima.'\nReply: Thanks, done. Please see lines 251–256: “During eccentricity minima, cooler\nand more stable climates, within a generally warm background, facilitated the\nexpansion of continental carbon reservoirs. This expansion led to greater land storage\nof isotopically light carbon and a corresponding rise in marine dissolved inorganic\ncarbon (δ¹³C-DIC), with the reverse occurring during maxima.”\n[84] Line 227-231: Please split the sentence and rephrase it.\nReply: Thanks, done. Please see lines 257–261: “Our results reveal the pronounced\nin-phase variation between the filtered long-eccentricity cycles and the amplitude\nmodulation of short eccentricity in the MS series over the CPE. This relationship\nsuggests that the higher values of the filtered eccentricity cycles are correlated with\nhigh eccentricity (corresponding to high variance of precession), and vice versa (Fig.\n2b).”\n[85] Line 229: 'suggest' instead of 'suggests'\nReply: Thanks, done. Please see line 259.\n[86] Line 246: Please add a comma before the word 'whereas' and apply this comment\nelsewhere in the text.\nReply: Thanks, done. Please see line 276.\n26\n[87] Line 247: Please change the punctuation 'e.g.' to 'e.g.,'\nReply: Thanks, we deleted the Carboniferous example. Please see line 276.\n[88] Line 254: Correct your spelling for the word 'approximatelly'\nReply: Thanks, done. Please see line 285.\n[89] Line 265: Typo: change the 'northestern' to 'northeastern' and apply this comment\nelsewhere in the text.\nReply: Thanks, done. Please see lines 299.\n[90] Line 275: Please add 'the' before the word 'implementation'\nReply: Thanks, done. Please see line 309.\n[91] Line 484: 'volcanic' instead of 'volcanics'\nReply: Thanks, done. Please see line 704.\n[92] Line 494: Please add 'the' before the word 'proportion'\nReply: Thanks, done. Please see line 713.\n[93] Line 517: Please add a preposition (an or the) before the word 'expansion'\nReply: Thanks, done. Please see line 740.\n[94] Line 520: The ‘Geological Setting’ is often treated as a standalone section,\nseparate from ‘Methodology’ because it provides critical context for the study area,\nwhich is important for interpreting results and is not typically considered part of the\nexperimental or analytical procedures.\nReply: Thank you very much. We moved this section to the maintext. Please see lines\n94–116.\n[95] Line 525: Please change the spelling: 'meters' instead of 'metres'\nReply: Thanks, 'meters' is British English, which is more in line with the style of\nNature Communications.\n[96] Line 525: Replace 'Formations' with 'formations' here and elsewhere in the text.\n[97] Line 541: There is structural issue in this section. The sentence ‘Organic-carbon\nisotopes and TOC contents (n = 289) were analyzed at the Nanjing Institute of\nGeology and Palaeontology, Chinese Academy of Sciences\" appears misplaced\nbecause it interrupts the logical flow of the sample preparation and analysis steps.\nReply: Thank you for pointing out the structural issue in this section. We have revised\nthe paragraph by moving the sentence “Organic-carbon isotopes and TOC contents (n\n= 289) were analyzed at the Nanjing Institute of Geology and Palaeontology, Chinese\nAcademy of Sciences” to the beginning of the paragraph. This adjustment ensures a\nmore logical flow in describing the sample preparation and analysis steps. Please see\nlines 329–331.\n[98] Line 543: Clarify what ‘n = 289’ refers to (e.g., total sample numbers) and\nspecify if it applies to δ¹³Corg, TOC, or both.\nReply: Thanks, we changed the sentence to \"Both organic-carbon isotopes (δ¹³C )\norg\nand TOC contents were analysed for a total of 289 samples at the Nanjing Institute of\nGeology and Palaeontology, Chinese Academy of Sciences.\" Please see lines 329–\n331.\n[99] Line 552: 'Were measured' instead of 'was measured'\nReply: Thanks, done. Please see line 340.\n[100] 590: Ensure the methodology section is structured consistently across all\nanalyses for clarity and readability (e.g., state the place of analysis, the number of\nsamples analyzed, the procedure, and the analytical precision).\nReply: Thank you for your constructive suggestion. I have revised the methodology\nsection to ensure consistency in structure across all analyses. For the elemental\nanalyses section, I have reorganised the text to clearly state the place of analysis, the\nnumber of samples analysed, the procedure, and the analytical precision and accuracy.\nThe revised section now follows a consistent format to enhance clarity and\nreadability. Please see lines 380–384: “Major and trace elements were analysed for a\ntotal of 154 samples at the Nanjing Institute of Geology and Palaeontology, Chinese\nAcademy of Sciences. An approximate 50 mg of sample powder was weighed and\n28\nashed at 110°C for 3 h. Then, the sample powder was digested in 1 ml of HNO and\n3\n1.5 ml of HF at 190°C for 72 h”.\n[101] Line 591: Please fix the typo: 'power' to 'powder'\nReply: Thanks, done. Please see line 382.\n[102] Line 591-592: I recommend re-phrase the sentence as follows: 'Then, the\nsample powder was digested in 1 ml of HNO3 and 1.5 ml of HF at 190°C for 72 h.'\nReply: Thanks, done. Please see lines 383–384.\n[103] Line 632: Correct the word 'ime'\nReply: Thank you. We correct the word to 'time'. Please see line 422.\n[104] Line 650: Correct the word 'temperatue'\nReply: Thanks, done. Please see line 443.\n[105] Line 659: Correct the word 'comparision'\nReply: Thanks, done. Please see line 453.\n[106] Line 692: Correct the word 'dicussions'\nReply: Thanks, done. Please see line 678.\n[107] Line 702: 'work' instead of 'works'\nReply: Thanks, done. Please see line 689.\n[108] Fig. 1: Please include the CPE record from the Miankuhi Formation, Turan\nPlate (NE Iran) based on recent study by Mazaheri-Johari et al. (2021, 2022).\nReply: Thanks, done. Please see Fig. 1.\n[109] Fig. 3: The figure caption states that 'S2: the Wrangellia LIP began releasing\nisotopically light carbon, POE appeared, and temperatures started to rise,' but the\nfigure lacks any temperature data/profile to support this. Since the manuscript\nincludes palynological studies suggesting a warm, arid climate during the δ¹³Corg\nfluctuations (POE to CIE2), it would be helpful to include temperature-related data in\n29\nthe figure or clarify how the temperature rise is being represented (e.g., using\nsupporting data from previous studies).\nReply: Thanks. We fully agree with you that adding a temperature curve would be\nbeneficial and attempted to do so. However, due to the high-resolution analysis in our\nstudy, we found that no palaeotemperature reconstruction work currently can offer the\nnecessary precision at this level, so we decided not to include it. In revision, we have\nadded the reference to Sun et al. (2016), which reconstructed palaeotemperature\ncurves based on oxygen isotopes from conodonts and supports the idea that\ntemperatures began to rise before the onset of CIE1. Please see line 724.\nSun, Y. D. et al. Climate warming, euxinia and carbon isotope perturbations during the\nCarnian (Triassic) crisis in South China. Earth Planet. Sci. Lett. 444, 88–100 (2016).\n[110] Fig. 3: show 'CIE interval' in the figure.\nReply: Thanks, added. Please see Fig. 3.\n[111] Fig. 4: Please mark the study area (Junggar Basin) on the figure (e.g., with a\nstar) to clarify the climate state in this basin before and during the CPE.\nReply: Thanks, added. Please see Fig. 4.\n[112] Table of Contents, Text S7: Correct the word ‘temperal’\nReply: Thanks, we have corrected \"spatial-temperal\" to \"spatial-temporal\".\n[113] Line 1: 'references' instead of 'reference'\nReply: Thanks, done. Please see line 1 in Supplementary Information.\n[114] Line 1: Eliminate the preposition 'on'\nReply: Thanks, done. Please see line 1 in Supplementary Information.\n[115] Line 55: Correct the words 'sandston' and 'sampless'\nReply: Thanks, done. Please see line 59 in Supplementary Information.\n[116] Line 65: 'was analyzed' instead of 'were analyzed'. Also apply the comment to\nline 70.\n[117] Line 92: Please add 'the' before 'Sliding window'\nReply: Thanks, done. Please see line 108 in Supplementary Information.\n[118] Line 93: Consider changing the verb form: 'are' instead of 'is'\nReply: Thanks, done. Please see line 109.\n[119] Line 131: Correct the words 'amplifing'\nReply: Thanks, done. Please see line 151.\n[120] Line 134: Correct the words 'eccenteicity'\nReply: Thanks, done. Please see line 154.\n[121] Line 138: Change the preposition: 'to the' instead of 'the'\nReply: Thanks, done. Please see line 158.\n[122] Line 141: 'intervals' instead of 'interval'\nReply: Thanks, done. Please see line 161.\n[123] Line 249: Change the punctuation: 'e.g.,' instead of 'eg.,'\nReply: Thanks, done. Please see line 271.\n[124] Line 265: Please add 'the' before the word 'potential'\nReply: Thanks, done. Please see line 287.\n[125] Line 275: 'Fig. S13' instead of 'Fig. S12'\nReply: Thanks, done. Please see line 297.\n[126] Line 277: Change 'on sample' to 'one sample'\nReply: Thanks, done. Please see line 299.\n[127] Line 278: Please consider re-phrasing, for example: 'Previous studies have\nshown that Hg behavior is non-linear with host-phase abundance, resulting in elevated\n31\nnormalized Hg values when host phase abundance is low (e.g., low TOC or low TS).'\nReply: Thanks, done. Please see lines 300–302: “Previous studies have shown that Hg\nbehavior is non-linear with host-phase abundance, resulting in elevated normalized\nHg values when host phase abundance is low (e.g., low TOC or low TS).”\n[128] Line 313: Correct the word 'measureable'\nReply: Thanks, done. Please see line 354.\n[129] Line 347: Remove the colon after the word 'including'\nReply: Thanks, done. Please see line 396.\n[130] Line 573: Correct the word 'Cretaceousi'\nReply: Thanks, done. Please see line 676.\n32"}, {"round": 2, "reviewer_comments": {"reviewer_1": "Dear authors,\nThanks for responding to my comments and revising the manuscript.\nAfter a careful read through the manuscript, I find it overall in good shape. I see most of my comments are addressed, but some are not ideally addressed.\nI don't understand the obsession with the methane hydrate. How much methane hydrate contributed the carbon isotope excursion in the Carnian, if at all? If this is not testable in this paper, it will only make the overall paper somewhat speculative.\nThe term ‘climate-carbon-cycle interaction’ is not easy to follow. The authors did a fair job explaining it in the reply letter, but not so perfectly in the manuscript. If I don't understand it, >90% of the audience won't understand.\nNevertheless, these are all my personal opinions, and I don't impose them on the authors. I only wish this manuscript to be amongst the best.", "reviewer_2": "The revised version needs to be improved from the following aspects:\n1) Line 103: silty or siltstone?\n2) Lines 103-109: The studied section is different from the section in Reference 42 or\nnot? If not, I strongly suggest that the authors add a lithological correlation map\nbetween two sections in the Supplementary Information and then mark the location of\nthe observed fossils.\n3) Line 119: sandstone or tuffaceous sandstone? Please clarify it. Why did you change\ntuffaceous sandstone to sandstone in the revised manuscript? If only the maximum\ndepositional age of the sandstone is considered, it is difficult to constrain the onset of\nthe CPE.\n4) Lines 141-143: You mean “the onset of CPE correspondsto a negative carbon isotope\nexcursion”? This is different with many previous studies.\n5) Lines 151-154: The authors need to explain why the studied section displayed a CIE\nwith an amplitude (6.5‰) larger than coeval sedimentary successions.", "reviewer_3": "Dear Editor, Dear Authors,\nI have reviewed the revised manuscript and I believe that the major points have been addressed by the authors. The\nmanuscript has now improved and can be considered for publication in this journal."}, "author_response": "RESPONSE TO REFEREES\nReference: NCOMMS-24-80380-A\nTitle: Climate–carbon-cycle interactions and spatial heterogeneity of the Carnian\nPluvial Episode (Late Triassic)\nJournal: Nature Communications\nWe thank the referees for their helpful comments that have greatly improved the\nquality of our interpretation and discussions of the Carnian Pluvial Episode. We have\nrevised the paper in line with these comments, focusing on moderating the speculative\ndiscussion on methane hydrates, improving clarity throughout the manuscript, and\nbetter integrating our findings within the context of previous studies. We outline\ndetailed responses to individual comments below.\nReviewer 1:\n[1] I don't understand the obsession with the methane hydrate. How much methane\nhydrate contributed the carbon isotope excursion in the Carnian, if at all? If this is not\ntestable in this paper, it will only make the overall paper somewhat speculative.\nReply: Thank you. We changed the sentence “Therefore, the isotopically light carbon\nreleased during CIE1 may have mainly originated from the dissociation of sub-ocean-\nfloor methane hydrates” to “Therefore, the dissociation of sub-ocean-floor methane\nhydrates might be an important source of the isotopically light carbon released during\nthe CIE1 (Fig. 3). Other feedback sources, such as peat and forest, could also\ncontribute to the supply of 13C-depleted carbon”. Please see lines 235–238.\n[2] The term ‘climate-carbon-cycle interaction’ is not easy to follow. The authors did a\nfair job explaining it in the reply letter, but not so perfectly in the manuscript. If I\ndon't understand it, >90% of the audience won't understand.\nReply: Thank you for pointing this out. To improve clarity, we have added a definition\nof this term in the revised manuscript, as follows: “Here, we use the term climate–\ncarbon-cycle interaction to describe the coupled feedback system in which climate\nvariables (e.g., temperature, hydrology and weathering) influence carbon-cycle\nprocesses (e.g., soil respiration, net primary productivity and CO₂ solubility), while\nthe carbon cycle, in turn, regulates global climate by modulating atmospheric\n1\ngreenhouse gas concentrations (CO₂ and CH₄)”, please see lines 252–257.\nReviewer 2:\n[3] Line 103: silty or siltstone?\nReply: Thanks. We changed the word “silty” to “siltstone”. Please see line 104.\n[4] Lines 103-109: The studied section is different from the section in Reference 42 or\nnot? If not, I strongly suggest that the authors add a lithological correlation map\nbetween two sections in the Supplementary Information and then mark the location of\nthe observed fossils.\nReply: Thank you very much. The studied section is the same as the section in\nReference 42. The author (Jungang Peng) of the Reference 42 is also the co-author of\nthis manuscript.\n[5] Line 119: sandstone or tuffaceous sandstone? Please clarify it. Why did you\nchange tuffaceous sandstone to sandstone in the revised manuscript? If only the\nmaximum depositional age of the sandstone is considered, it is difficult to constrain\nthe onset of the CPE.\nReply: Thank you for your comment. Initially, we identified the samples as tuffaceous\nsandstone because the zircon ages yielded from LA-ICP-MS U-Pb dating were highly\nconcentrated, suggesting a possible volcanic origin. In the first round of review, you\nkindly suggested that we add a micrograph of the dated sample. We specifically\nconducted an additional field trip to Xinjiang to recollect samples. We then prepared\nthin sections and obtained a detailed photomicrograph (now included as Fig. S1).\nAfter careful petrographic examination and discussions with petrology experts, we\nrevised the lithological classification to sandstone.\nAlthough sandstone can only provide a maximum depositional age, in this case,\nthe combined biostratigraphic and radiometric evidence is sufficient to constrain the\nonset of the CPE, as follows: (1) the vertebrate Fukangichthys fauna and\npalynological zonation (including Aratrisporites, Dictyophyllidites-Aratrisporites, and\nLycopodiacidites-Stereisporites) suggest that the boundary between the Middle and\nUpper Triassic (~ 237 Ma) lies between the uppermost Karamay Formation and the\nbase of the Huangshanjie Formation; (2) The U-Pb age obtained from the lower\nHuangshanjie Formation yield a maximum depositional age of 232.9 ± 0.7 Ma,\n2\nindicating that the true depositional age of this horizon must be equal to or younger\nthan 232.9 ± 0.7 Ma. Therefore, the onset of the CPE (approximately 234 Ma) must\nfall between the Middle-Upper Triassic boundary (237 Ma) and the dated horizon at\n232.9 ± 0.7 Ma. We changed the sentence “These absolute ages place the CPE (234–\nstratigraphic level of the sample with the youngest depositional age of 232 Ma)” to\n“These absolute ages place the onset of the CPE (approximately 234 Ma) between the\nMiddle-Upper Triassic boundary (237 Ma) and the stratigraphic level of the sample\nwith the youngest depositional age of 232.9 ± 0.7 Ma” to make the statement more\nconcise. Please see lines 114–117.\nBased on this stratigraphic framework, we further use carbon-isotopes data to\npinpoint the onset of the CPE more precisely.\n[6] Lines 141-143: You mean “the onset of CPE correspondsto a negative carbon\nisotope excursion”? This is different with many previous studies.\nReply: Thanks a lot for your comment. Yes, here we mean that the onset of CPE\ncorresponds to a negative carbon-isotope excursion (CIE). This CIE has been\nconsistently identified across a wide range of depositional settings, including the\nTethyan Ocean (e.g., Dal Corso et al., 2012, 2018; Mueller et al., 2016a; Sun et al.,\n2016), the Boreal realm (Mueller et al., 2016b), and the continental interiors of\nPangea (e.g., Baranyi et al., 2019; Lu et al., 2021; Miller et al., 2017), indicating a\nglobally carbon cycle perturbation at the onset of the CPE. Importantly, previous\nstudies have shown that this CIE coincided with a transition to siliciclastic-dominated\nsedimentation, and a marked shift in carbonate production mode—from microbially\ninduced carbonate precipitation to metazoan biomineralization (Please see Dal Corso\net al., 2018).\nBased on a well-constrained chronological framework, we further emphasise that\nreliable and unaltered carbon-isotope records should serve as the primary stratigraphic\ntool for high-resolution correlation of the CPE. Because carbon isotopes reflect global\nperturbations in the carbon cycle, with CO₂ circulating throughout the ocean–\natmosphere–terrestrial system, thus providing a more globally coherent signal. In\ncontrast, humidity changes are inherently regional and cannot be expected to occur\nsynchronously or uniformly across all palaeogeographic settings. As demonstrated in\n3\nour study, not all regions experienced increased humidity during the CPE,\nunderscoring that the negative CIE is a more robust and diagnostic marker for\nrecognising and correlating the event on a global scale.\nBaranyi, V., Miller, C. S., Ruffell, A., Hounslow, M. W. & Kürschner, W. M. A\ncontinental record of the Carnian Pluvial Episode (CPE) from the Mercia\nMudstone Group (UK): palynology and climatic implications. J. Geol. Soc.\nLondon 176, 149–166 (2019).\nDal Corso, J. et al. Discovery of a major negative 13C spike in the Carnian (Late\nTriassic) linked to the eruption of Wrangellia flood basalts. Geology 40, 79–82\n(2012).\nDal Corso, J. et al. Multiple negative carbon-isotope excursions during the Carnian\nPluvial Episode (Late Triassic). Earth Sci. Rev. 185, 732–750 (2018).\nLu, J. et al. Volcanically driven lacustrine ecosystem changes during the Carnian\nPluvial Episode (Late Triassic). Proc. Natl. Acad. Sci. U.S.A. 118, e2109895118\n(2021).\nMueller, S., Krystyn, L. & Kürschner, W. M. Climate variability during the Carnian\nPluvial Phase—a quantitative palynological study of the Carnian sedimentary\nsuccession at Lunz am See, Northern Calcareous Alps, Austria. Palaeogeogr.\nPalaeoclimatol. Palaeoecol. 441, 198–211 (2016a).\nMueller, S., Hounslow, M.W. & Kürschner, W.M. Integrated stratigraphy and\npalaeoclimate history of the Carnian Pluvial Event in the Boreal realm: new data\nfrom the Upper Triassic Kapp Toscana Group in central Spitsbergen (Norway). J.\nGeol. Soc. London 173, 186–202 (2016b).\nMiller, C. S. et al. Astronomical age constraints and extinction mechanisms of the\nLate Triassic Carnian crisis. Sci. Rep. 7, 2557 (2017).\nSun, Y. D. et al. Climate warming, euxinia and carbon isotope perturbations during the\nCarnian (Triassic) crisis in South China. Earth Planet. Sci. Lett. 444, 88–100\n(2016).\n4\n[7] Lines 151-154: The authors need to explain why the studied section displayed a\nCIE with an amplitude (6.5‰) larger than coeval sedimentary successions.\nReply: Thank you very much for your comment. Variability in carbon isotope\nexcursion (CIE) amplitude is commonly observed in the geological record, including\nwell-studied events such as the Paleocene-Eocene Thermal Maximum (PETM), where\nthe magnitude of the negative δ¹³C excursion varies significantly across different\nsedimentary records and substrates (McInerney & Wing, 2011; Sluijs & Dickens,\n2012). Such variability reflects the influence of multiple factors, including organic\nmatter source, depositional environment, diagenesis, and photosynthetic pathways\n(Dal Corso et al., 2017, 2018; Diefendorf et al., 2010). Therefore, direct comparison\nof CIE amplitudes across terrestrial and marine records must be made with caution,\nand the amplitude alone is not a diagnostic indicator of the carbon source.\nIn the previous version, we have included a discussion of the relatively large\namplitude (~6.5‰) observed in our studied section in the Supplementary Information.\nPlease see lines 259–266 for “Compound-specific long-chain n-alkane (C –C ) δ13C\n23 31\nvalues in the DLK section show both a distinct ∼6.5‰ negative isotopic excursion\nand a ∼4.0‰ negative isotopic excursion, corresponding to the bulk δ13C CIE1 and\norg\nCIE2, respectively (Fig. S12). This result indicates that carbon-cycle perturbations in\nthe atmosphere are consistent with the bulk δ13C in the lacustrine deposits,\norg\nsuggesting that the mix of organic matter from algae, pollen and spores, waxy leaf and\nwood could have amplified the magnitude by a few permil compared to the average\n~3–4‰ CIE1 in marine deposits (Dal Corso et al., 2018)”.\nDal Corso, J. et al. Evaluating the use of amber in palaeoatmospheric reconstructions:\nthe carbon-isotope variability of modern and Cretaceous conifer resins. Geochim.\nCosmochim. Acta 199, 351–369 (2017).\nDal Corso, J. et al. Multiple negative carbon-isotope excursions during the Carnian\nPluvial Episode (Late Triassic). Earth Sci. Rev. 185, 732–750 (2018).\nDiefendorf, A.F. et al. Global patterns in leaf 13C discrimination and implications for\nthe studies of past and future climate. Proc. Nat. Acad. Sci. U. S. A. 107, 5738–\n5743 (2010).\nMcInerney, F.A. & Wing, S. L. The Paleocene-Eocene thermal maximum: a\nperturbation of carbon cycle, climate, and biosphere with implications for the\n5\nfuture. Annu. Rev. Earth Planet. Sci. 39, 489–516 (2011).\nSluijs, A. & Dickens, G. R. Assessing offsets between the δ13C of sedimentary\ncomponents and the global exogenic carbon pool across early Paleogene carbon\ncycle perturbations. Glob. Biogeochem Cycles 26, GB4005 (2012).\nReviewer 3:\n[8] I have reviewed the revised manuscript and I believe that the major points have\nbeen addressed by the authors. The manuscript has now improved and can be\nconsidered for publication in this journal.\nReply: Thank you very much.\n6"}]

Decision letter