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The Common Era history of effective moisture in the Central Andes is poorly understood, as most Andean proxy records reflect large-scale atmospheric circulation over the South American lowlands rather than localized precipitation vs. evaporation. Here we present 1800-year leaf wax hydrogen and carbon isotope sedimentary records from Lake Chacacocha (13.96°S, 71.08°W, 4,860 m asl.) in the Central Andes. Leaf wax δ2H from different chain lengths offers information about large-scale atmospheric conditions and local-scale effective moisture. Our leaf wax δ2H data record a gradual intensification of the South American summer monsoon (SASM) beginning around ~1250 CE, prior to the external forcings of the Little Ice Age (LIA). Despite peak SASM intensification, our leaf wax δ13C data reveal a locally arid interval between ca. 1600 and 1800 CE. The arid interval was most likely driven by enhanced evaporation and reduced local precipitation, as indicated by the hydrogen isotope fractionation between mid- and long-chain n-alkanes as well as by climate model simulations. Our results help to reconcile conflicting interpretations of the SASM, glacial, and lake-level histories in the Central Andes during the Common Era. 

Abstract Climate‐driven thawing of Arctic permafrost renders its vast carbon reserves susceptible to microbial degradation, serving as a potentially potent positive feedback hidden within the climate system. While seemingly intuitive, the relationship between thermally driven permafrost losses and organic carbon (OC) export remains largely unexplored in natural settings. Filling this knowledge gap, we present down‐core bulk and compound‐specific radiocarbon records of permafrost change from a sediment core taken within the Alaskan Colville River delta spanning the lastc. 2,700 years. Fingerprinted by significantly older radiocarbon ages of bulk OC and long‐chain fatty acids, these data expose a thermally driven increase in permafrost OC export and/or deepening of mobilizable permafrost layers over the lastc. 160 years after the Little Ice Age. Comparison of OC content and radiocarbon data between recent and Roman warming episodes likely implies that the rate of warming, alongside the prevailing boundary conditions, may dictate the ultimate fate of the Arctic's permafrost inventory. Our findings highlight the importance of leveraging geological records as archives of Arctic permafrost mobilization dynamics with temperature change.