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Abstract Rapid Arctic warming this century will likely cause major water cycle and atmospheric circulation changes, including weakening mid‐latitude westerly winds and more persistent summer high pressures over Fennoscandia. These conditions can cause drought in northern Europe and extreme rainfall in the Mediterranean region. Uncertainties in the spatiotemporal patterns of these predictions can be partially addressed with records of past climate response to rapid change. The early Holocene collapse of the Northern Hemisphere ice sheets provides a natural experiment to evaluate the climate response to rapid changes in boundary conditions. We analyzed lipid biomarker distributions and hydrogen isotope (δ²H) values from Lake Imandra, Kola Peninsula, to infer Holocene summer temperature and summer precipitation δ²H values. Sensitivity tests of a lake model suggest summer precipitation δ²H values are the main mechanism influencing Lake Imandra δ²H values. Summer precipitation isotope values exhibited a nearly 20‰²H‐depletion between 8.6 and 8.0 ka, with²H ‐enriched values before 8.6 ka and²H ‐depleted values 8.0 ka to present. Maximum warmth occurred from 8.5 to 7.0 ka. Climate model experiments suggest that the early Holocene Laurentide Ice Sheet collapse caused a westward shift of the Fennoscandian summer high‐pressure center. This caused a decrease in the proportion of local,²H‐enriched precipitation falling throughout Fennoscandia and an increase in far‐traveled,²H‐depleted precipitation from the mid‐latitudes, circulation that persisted throughout the Holocene. These results illustrate the sensitivity of climate in Fennoscandia and show that circulation regime shifts can occur in response to changes in boundary conditions far upwind. 

Abstract Changes in ice‐sheet size impact atmospheric circulation, a phenomenon documented by models but constrained by few paleoclimate records. We present sub‐centennial‐scale records of summer temperature and summer precipitation hydrogen isotope ratios (δ²H) spanning 12–7 ka from a lake on Baffin Island. In a transient model simulation, winds in this region were controlled by the relative strength of the high‐pressure systems and associated anticyclonic circulation over the retreating Greenland and Laurentide ice sheets. The correlation between summer temperature and precipitation δ²H proxy records changed from negative to positive at 9.8 ka. This correlation structure indicates a shift from alternating local and remote moisture, governed by the two ice‐sheet high‐pressure systems, to only remote moisture after 9.8 ka, governed by the strong Greenland high‐pressure system after the Laurentide Ice Sheet retreated. Such rapid atmospheric circulation changes may also occur in response to future, gradual ice‐sheet retreat. 

Abstract Quantitative temperature reconstructions from lacustrine organic geochemical proxies including branched glycerol dialkyl glycerol tetraethers (brGDGTs) and alkenones provide key constraints on past continental climates. However, estimation of air temperatures from proxies can be impacted by non‐stationarity in the relationships between seasonal air and water temperatures, a factor not yet examined in strongly seasonal high‐latitude settings. We pair downcore analyses of brGDGTs and alkenones measured on the same samples through the Holocene with forward‐modeled proxy values based on thermodynamic lake model simulations for a western Greenland lake. The measured brGDGT distributions suggest that stable autochthonous (aquatic) production overpowers allochthonous inputs for most samples, justifying the use of the lake model to interpret temperature‐driven changes. Conventional calibration of alkenones (detected only after 5.5 thousand years BP) suggests substantially larger temperature variations than conventional calibration of brGDGTs. Comparison of proxy measurements to forward‐modeled values suggests variations in brGDGT distributions monotonically reflect multi‐decadal summer air temperatures changes, although the length of the ice‐free season dampens the influence of air temperatures on water temperatures. Drivers of alkenone variability remain less clear; potential influences include small changes in the seasonality of proxy production or biases toward specific years, both underlain by non‐linearity in water‐air temperature sensitivity during relevant seasonal windows. We demonstrate that implied temperature variability can differ substantially between proxies because of differences in air‐water temperature sensitivity during windows of proxy synthesis without necessitating threshold behavior in the lake or local climate, and recommend that future studies incorporate lake modeling to constrain this uncertainty. 

ABSTRACT The Russian Arctic is an extensive region, with relatively few long‐duration paleoclimate reconstructions compared to other terrestrial Arctic regions. We present a 24 000‐year reconstruction of climate in the Polar Ural Mountains usingn‐alkanoic acid hydrogen isotopes from Lake Bolshoye Shchuchye. Major last deglaciation climate changes in the North Atlantic are present in this record, including transitions associated with the Bølling–Allerød, Younger Dryas and Holocene. However, the magnitude of the last deglaciation isotopic shifts at Bolshoye Shchuchye are small relative to the North Atlantic, and are dwarfed by a shift to²H‐enriched values starting at 10.5k cal abpat this site that is not present in most other records. The last deglaciation changes may be due to variations in local temperature, sea ice cover in the Barents and Kara seas, and plant community shifts impacting transpiration. The enrichment starting at 10.5‐k cal abpprobably records a shift towards modern climate conditions, caused by the loss of the Scandinavian Ice Sheet, increased locally sourced moisture from the Barents and Kara seas, and northward treeline migration causing enhanced transpiration. Future warming may increase summer precipitation in this region, with changes to local ecosystems and carbon cycling.