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The effect of plant type on n-alkane biomarker has been widely studied, but the influence of plant type on n-alkanoic acids (n-FAs) has received less attention. Understanding the effect of the distribution of n-FAs and their hydrogen isotope composition (δ2HFA) is critical for interpreting sedimentary δ2HFAvalues as proxies of hydroclimate and/or vegetation changes. In this study, we systematically investigated the distribution of n-FAs and δ2HFAvalues across seasons on the Chinese Loess Plateau (CLP). Our results showed that there were no significant seasonal differences in n-FAs distribution and δ2HFAvalues, but there were significant differences in δ2HFAvalues across plant types. The δ2HFAvalues ranged from −185‰ to −125‰ in dicots (−161‰±28‰), and from −215‰ to −170‰ in monocots (−196‰±22‰) on the CLP. Isotope fractionation between δ2HFAvalues and precipitation δ2H (εFA-P) was also 2H-enriched in dicots relative to monocots. At the regional scale of the CLP, δ2HFAvalues were not correlated with δ2H values of precipitation. However, δ2HFAvalues from the CLP were similar to expectations from a global comparison, both in terms of their mean values and high variability among plants growing in sites with similar δ2H values of precipitation. As some of this variability in εFA-Pis due to the effect of plant type, a careful assessment of the likely sources of waxes in terrestrial sediments is critical when using δ2HFAvalues for paleohydroclimate reconstruction.

Sihailongwan Maar Lake, located in Northeast China, is a candidate Global boundary Stratotype Section and Point (GSSP) for demarcation of the Anthropocene. The lake’s varved sediments are formed by alternating allogenic atmospheric inputs and authigenic lake processes and store a record of environmental and human impacts at a continental-global scale. Varve counting and radiometric dating provided a precise annual-resolution sediment chronology for the site. Time series records of radioactive (239,240Pu, 129I and soot 14C), chemical (spheroidal carbonaceous particles, polycyclic aromatic hydrocarbons, soot, heavy metals, δ13C, etc.), physical (magnetic susceptibility and grayscale) and biological (environmental DNA) indicators all show rapid changes in the mid-20th century, coincident with clear lithological changes of the sediments. Statistical analyses of these proxies show a tipping point in 1954 CE. 239,240Pu activities follow a typical unimodal globally-distributed profile, and are proposed as the primary marker for the Anthropocene. A rapid increase in 239,240Pu activities at 88 mm depth in core SHLW21-Fr-13 (1953 CE) is synchronous with rapid changes of other anthropogenic proxies and the Great Acceleration, marking the onset of the Anthropocene. The results indicate that Sihailongwan Maar Lake is an ideal site for the Anthropocene GSSP.

Intrashell oxygen isotope (δ18Os) analyses of terrestrial snails have been carried out over two decades. However, the intraspecies/interspecies differences are not yet well understood. Here, we conducted a high‐resolution intrashell δ18Osstudy on 43 shells from Cathaica fasciolaand Bradybaena ravida, and 1449 δ18Osdata were obtained. These large amounts of data demonstrate the reproducibility of intrashell δ18Os. Our results suggest that C. fasciolaand B. ravidahave similar growing seasons mainly from March to October in the studied region. The ecological habits of the two species could explain the distinctive variations in their δ18Ossequences. Therefore, our study may interpret the discrepancy between the studies of land snail species and the stable/clumped isotopes of their shells. Moreover, the calculated average growth rate is ∼290 μm/day (from 250 to 330 μm/day) for nonadult C. fasciola. Thus, the use of snail shells for reconstructing high‐resolution terrestrial climate changes is promising. Land snails are sensitive to climatic and environmental changes. Therefore, the oxygen isotopic composition of snail shells (δ18Os) has often been used to study environmental changes. Researchers started to collect multiple samples from a single shell for δ18Osanalyses about two decades ago. However, it is still unclear whether high‐resolution intrashell δ18Osresults are repeatable and whether the influences of different individuals/species may exist. To address these issues, we collected 43 snail shells from Cathaica fasciolaand Bradybaena ravida. In total, 1449 δ18Osdata were obtained. The large amount of data showing similar variations in the intrashell δ18Osfrom different shells demonstrates the repeatability. Accordingly, our data suggest that the two species have similar growing seasons, mainly from March to October, although their ecological habits are different. In addition, the ecological habits of these two species could explain the subtle differences in their δ18Os. Taken together, our study could resolve the discrepancy between previous work on land snail species and stable/clumped isotopes. Furthermore, the estimated average growth rate is ∼290 μm/day (from 250 to 330 μm/day) for nonadult C. fasciola. Overall, snail shells are promising records for exploring high‐resolution terrestrial climate changes in the future. The intrashell δ18Osof land snails is reproducible, which mainly records the δ18O of precipitationCathaica fasciolaand Bradybaena ravidahave different ecological habits but similar growing seasonEcological habits could explain the discrepancy between studies of land snail species and stable/clumped isotopes The intrashell δ18Osof land snails is reproducible, which mainly records the δ18O of precipitation Cathaica fasciolaand Bradybaena ravidahave different ecological habits but similar growing season Ecological habits could explain the discrepancy between studies of land snail species and stable/clumped isotopes

The hydrogen isotopic composition (δD) of n-alkanes in lacustrine sediments is widely used in palaeoenvironmental studies, but the heterogeneous origins and relative contributions of these lipids provide challenges for the interpretation of the increasing dataset as an environment and climatic proxy. We systematically investigated n-alkane δD values from 51 submerged plants (39 Potamogeton, 1 Myriophyllum, and 11 Ruppia), 13 algae (5 Chara, 3 Cladophora, and 5 Spirogyra) and 20 terrestrial plants (10 grasses and 10 shrubs) in and around 15 lakes on the Tibetan Plateau. Our results demonstrate that δD values of C29n-alkane are correlated significantly with the lake water δD values both for algae (R2=0.85, p<0.01, n=9) and submerged plants (R2=0.90, p<0.01, n=25), indicating that δD values of these algae and submerged plants reflect the δD variation of lake water. We find that apparent hydrogen isotope fractionation factors between individual n-alkanes and water (εa/w) are not constant among different algae and submerged plants, as well as in a single genus under different liminological conditions, indicating that the biosynthesis or environmental conditions (e.g. salinity) may affect their δD values. The δD values of submerged plant Ruppiain the Xiligou Lake (a closed lake) are significant enriched in D than those of terrestrial grasses around the lake (one-way ANOVA, p<0.01), but the algae Charain the Keluke Lake (an open lake) display similar δD values with grasses around the lake (one-way ANOVA, p=0.826>0.05), suggesting that the n-alkane δD values of the algae and submerged plants record the signal of D enrichment in lake water relative to precipitation only in closed lakes in arid and semi-arid area. For each algae and submerged plant sample, we find uniformed δD values of different chain length n-alkanes, implying that, in combination with other proxies such as Paq and Average Chain Length, the offset between the δD values of different chain length n-alkanes can help determine the source of sedimentary n-alkanes as well as inferring the hydrological characteristics of an ancient lake basin (open vs closed lake).

Contrasting moisture evolutions between westerlies‐dominated Central Asia and monsoonal Asia since the mid‐Holocene have been widely recognized. Yet, inconsistent hydrological records over the early Holocene from both regions hamper our understanding of hydroclimatic changes and associated mechanisms. Here we present isotopic and biomarker (alkenone) records from three Chinese lakes located at both regions to address a possible meltwater role in lake water budget. Our results show the occurrence of particularly depleted isotopic values of lake water associated with lake freshening within the deglaciation and early Holocene. Together with anomalously old 14C dates, which were also documented in many other Asian lakes, our observations likely indicate substantial meltwater contribution to mid‐latitude Asian lake water budget, along with the climatic warming. Hence, the potential meltwater effect should be considered when inferring Asian summer monsoon and westerlies behavior over this critical period, with important implications to Holocene hydrological reconstructions and future hydroclimatic projections. Although meltwater events have been well documented in marine records, the effects of meltwater on Asian lake water budget and regional hydrological cycle during the deglaciation and warm early Holocene remain poorly investigated. Our isotopic and biomarker records from Lake Sayram, Yanhaizi, and Qinghai in northern China, together with anomalously old 14C dates from investigated lakes and other Asian lakes, likely indicate substantial meltwater contribution to lake water budget within the deglaciation and early Holocene, which appears to be a large‐scale phenomenon in mid‐latitude Asia. This suggests that the potential meltwater effect on Asian lake hydrology should be assessed in climatic reconstructions and simulations, which may shed light on accurate interpretation of westerlies and summer monsoon circulation over the early Holocene. Isotopic records likely indicate meltwater contribution to Asian lake water budget within the deglaciation and early HoloceneAnomalously old 14C dates summarized from mid‐latitude Asian lakes also support substantial meltwater input during this periodMeltwater effects should be considered when inferring early Holocene Asian summer monsoon and westerlies behavior Isotopic records likely indicate meltwater contribution to Asian lake water budget within the deglaciation and early Holocene Anomalously old 14C dates summarized from mid‐latitude Asian lakes also support substantial meltwater input during this period Meltwater effects should be considered when inferring early Holocene Asian summer monsoon and westerlies behavior

The hydrogen isotopic composition (δD) of leaf wax long-chain n-alkanes (C27, C29, and C31) from lacustrine sediments has been widely applied to reconstruct terrestrial paleoclimatic and paleohydrological changes. However, few studies have addressed whether the aquatic-derived n-alkanes can affect the δD values of lake sedimentary long-chain n-alkanes, which are usually regarded as a recorder of the terrestrial hydrological signals. Here we systematically investigated δD values of long-chain n-alkanes from modern aquatic plants, both near-shore and off-shore surface sediments, surrounding terrestrial plant litters, as well as river water and lake water in Lake Qinghai and its satellite lakes on the northeastern Qinghai-Tibet Plateau. Our data showed that (i) δD values of long-chain n-alkanes from aquatic plants varied from -184‰ to -132‰ for n-C27, from -183‰ to -138‰ for n-C29, and from -189‰ to -130‰ for n-C31, respectively, with no significant differences among the three n-alkanes homologues; (ii) δD values of long-chain n-alkanes from aquatic plants were generally more positive than those from surrounding terrestrial plants, possibly because that they recorded the D-enrichment of lake water in this semi-arid region; (iii) δD values of long-chain n-alkanes from surface sediments showed significant differences among the three n-alkanes homologues, due to the larger aquatic input of n-C27to the sedimentary lipid pool than that of n-C31, and (iv) n-C27δD values of near-shore aquatic plants and near-shore sediments are more negative than those from off-shore as a result of lower δD values of near-shore lake water. Our findings indicate that in this region (i) the offset between sedimentary n-C27and n-C31δD values (ΔδDC27-C31) could potentially be used to evaluate if sedimentary long-chain n-alkanes are derived from a single source; (ii) while δD values of n-C27may be influenced by lake water hydrological changes, sedimentary n-C31is derived predominantly from terrestrial plants and thus its δD can serve as a relatively reliable indicator for terrestrial paleoclimatic and paleohydrological reconstructions.

Record of long‐term land temperature changes remains ephemeral, discontinuous, and isolated, thus leaving the common view that Pleistocene land temperature evolution should have followed ocean temperatures unconfirmed. Here, we present a continuous land surface temperature reconstruction in the Asian monsoon region over the past 3.0 Myr based on the distribution of soil bacterial lipids from the Chinese Loess Plateau. The land temperature record indicates an unexpected warming trend over the Pleistocene, which is opposite to the cooling trend in Pleistocene ocean temperatures, resulting in increased land‐sea thermal contrast. We propose that the previously unrecognized increase of land‐sea thermal contrast during much of the Pleistocene is a regional climate phenomenon that provides a likely mechanism in favor of the long‐term enhancement of the Pleistocene East Asian summer monsoon. Numerous sea surface temperature (SST) records indicate long‐term gradual cooling over the Pleistocene, whereas the East Asian summer monsoon (EASM) appears to have strengthened during this period. Land‐sea thermal contrast is thought to have an important influence on the intensity of the EASM, but the lack of land surface temperature (LST) records from monsoonal regions prevents the assessment of its role in driving monsoonal changes. Here, we present a 3‐Myr‐long LST record from the Chinese Loess Plateau, displaying a unique long‐term warming trend over the Pleistocene, different from the trajectories of SST records. We propose that the decoupling of long‐term land and sea temperatures, and thus the increase of land‐sea thermal contrast, provides a simple interpretation for the otherwise paradox, strengthening of the EASM over the Pleistocene. This study presents much needed original LST data that support novel interpretations on a mechanism for important paleoclimate phenomenon in East Asia with implications to the entire terrestrial ecosystem during the critical period of earth history. Three million years of continuous land surface temperatures reconstructed based on soil bacterial lipidsThe land temperature record indicates an unexpected warming trend over the PleistoceneIncreasing land‐sea thermal contrast facilitated the long‐term intensification of Pleistocene East Asian summer monsoon Three million years of continuous land surface temperatures reconstructed based on soil bacterial lipids The land temperature record indicates an unexpected warming trend over the Pleistocene Increasing land‐sea thermal contrast facilitated the long‐term intensification of Pleistocene East Asian summer monsoon