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The scarcity of research in NE China on lake ecosystem responses to large-scale climate oscillations since the last deglaciation limits our abilities for informing conservation practices and policies in the context of recent global warming. Here, a high-resolution, sedimentary diatom record covering the past ∼17,500 years was retrieved from Lake Moon, a small, hydrologically closed crater lake in the remote central part of the Great Khingan Mountain Range in NE China. We compare diatom changes with geochemical data from the same core, and with regional palynological and dust deposition records, to better understand the influences of long-term environmental and climatic variability on aquatic ecosystems in this climatically sensitive region. Several abrupt and pronounced shifts in dominance among diatom taxa corresponded to marked fluctuations in the climate regime since the last deglaciation. During the close of the Last Glacial Period, a series of short-lived diatom shifts that were indicative of an increase in nutrients, signaled the transition from the cold period of the Heinrich event 1 (∼17,500–∼14,700 cal yr BP) to the warmer Bolling - Allerod interstadial period (∼14,700–∼12,900 cal yr BP). The onset of the cold Younger Dryas period was marked by a brief rise to dominance of benthic taxa (∼12,900–∼11,800 cal yr BP), followed by a pronounced lake ecosystem shift to a new trophic state at the Pleistocene-Holocene transition (∼11,800–∼9900 cal yr BP), evidenced by an abrupt rise to dominance of several eutrophic diatom indicators (e.g. Cyclostephanos dubius, Aulacoseira ambigua and Stephanodiscus parvus). This nearly complete compositional turnover was indicative of an increase in phosphorus supply to the lake with the onset of a warmer and moister climate and an increased frequency of strong dust storms. During the mid-Holocene (∼6000 cal yr BP), a striking increase in the relative abundance of Discostella pseudostelligera and Asterionella formosa, at the expense of previously dominant eutrophic indicators, signified another lake ecosystem change from well-mixed, turbid and phosphorus-rich conditions to a lower nutrient state with longer open-water periods and increased thermal stability. The turnover to oligotrophic diatom taxa was likely in response to variations in seasonal temperature, precipitation and dust deposition. The diatom shifts of Lake Moon during the past ∼17,500 years were directly or indirectly mediated by climate change that affected thermal stratification, productivity, lake level and trophic state. Our results indicate that climate change had an overarching control on aquatic ecosystem changes in the mountain regions of NE China since the last deglaciation.

The spatio-temporal pattern of peak Holocene warmth (Holocene thermal maximum, HTM) is traced over 140 sites across the Western Hemisphere of the Arctic (0–180°W; north of ∼60°N). Paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer-than-present conditions at 120 of these sites. At the 16 terrestrial sites where quantitative estimates have been obtained, local HTM temperatures (primarily summer estimates) were on average 1.6±0.8°C higher than present (approximate average of the 20th century), but the warming was time-transgressive across the western Arctic. As the precession-driven summer insolation anomaly peaked 12–10 ka (thousands of calendar years ago), warming was concentrated in northwest North America, while cool conditions lingered in the northeast. Alaska and northwest Canada experienced the HTM between ca 11 and 9 ka, about 4000 yr prior to the HTM in northeast Canada. The delayed warming in Quebec and Labrador was linked to the residual Laurentide Ice Sheet, which chilled the region through its impact on surface energy balance and ocean circulation. The lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change. The spatial asymmetry of warming during the HTM resembles the pattern of warming observed in the Arctic over the last several decades. Although the two warmings are described at different temporal scales, and the HTM was additionally affected by the residual Laurentide ice, the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing. Unlike the HTM, however, future warming will not be counterbalanced by the cooling effect of a residual North American ice sheet.