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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 Sedimentary plant waxδ²H values are common proxies for hydrology, a poorly constrained variable in the Arctic. However, it can be difficult to distinguish plant waxes derived from aquatic versus terrestrial plants, causing uncertainty in climate interpretations. We test the hypothesis that Arctic lake sediment mid‐ and long‐chain plant waxes derive from aquatic and terrestrial plants, respectively. We comparen‐alkanoic acid andn‐alkane chain‐length distributions andn‐alkanoic acidδ²H andδ¹³C values of the 29 most abundant modern plant taxa to those for soils, water filtrates, and lake sediments in the Qaupat Lake (QPT) catchment, Nunavut, Canada. Chain length distributions are variable among terrestrial plants, but similar and dominated by mid‐chain waxes among submerged/floating aquatic plants. Sedimentary wax distributions are similar to those in submerged/floating aquatic plants and toSalixspp., which are among the most abundant terrestrial plants in the QPT catchment. Mid‐chainn‐alkanoic acidδ²H values are similar in sediments and submerged/floating aquatic plants, but 50‰ lower thanSalixspp. In contrast, sedimentary long‐chainn‐alkanoic acidδ²H values fall between those for submerged/floating aquatic plants andSalixspp. We therefore infer that mid‐chain waxes in QPT are primarily from aquatic plants, whereas long‐chain waxes are from a mix of terrestrial and aquatic plants. In Arctic lakes like QPT, terrestrial wax transport via leaf litter and surface flow is limited by low‐lying topography and sparse vegetation. If these lakes also have abundant aquatic plants growing near the sediment‐water interface, the aquatic plants can contribute large portions of sedimentary waxes. 

Abstract Lacustrine δ²H and δ¹⁸O isotope proxies are powerful tools for reconstructing past climate and precipitation changes in the Arctic. However, robust paleoclimate record interpretations depend on site‐specific lake water isotope systematics, which are poorly described in the eastern Canadian Arctic due to insufficient modern lake water isotope data. We use modern lake water isotopes (δ¹⁸O and δ²H) collected between 1994–1997 and 2017–2021 from a transect of sites spanning a Québec‐to‐Ellesmere Island gradient to evaluate the effects of inflow seasonality and evaporative enrichment on the δ²H and δ¹⁸O composition of lake water. Four lakes near Iqaluit, Nunavut sampled biweekly through three ice‐free seasons reflect mean annual precipitation isotopes with slight evaporative enrichment. In a 23° latitudinal transect of 181 lakes, through‐flowing lake water δ²H and δ¹⁸O fall along local meteoric water lines. Despite variability within each region, we observe a latitudinal pattern: southern lakes reflect mean annual precipitation isotopes, whereas northern lakes reflect summer‐biased precipitation isotopes. This pattern suggests that northern lakes are more fully flushed with summer precipitation, and we hypothesize that this occurs because the ratio of runoff to precipitation increases with latitude as vegetation cover decreases. Therefore, proxy records from through‐flowing lakes in this region should reflect precipitation isotopes with minimal influence of evaporation, but vegetation changes in lake catchments across a latitudinal transect and through geologic time may influence the seasonality of lake water isotopic compositions. Thus, we recommend that future lake water isotope proxy records are considered in context with temperature and ecological proxy records. 

Recent anthropogenic warming in the Arctic has caused accelerated permafrost thaw, leading to the export of relict organic carbon (OC) to the atmosphere and surrounding depositional environments. Past episodes of warmth exceeding pre-industrial temperatures, such as the Holocene Thermal Maximum (HTM; 11 to 8 kiloannum (ka) at our study site), may serve as an analogue for how the Arctic carbon cycle responds to ongoing warming. We reconstructed accumulation rates of three OC endmembers (contemporaneous aquatic biomass, postglacial soil, and MIS 5 soil) at Lake CF8, northeastern Baffin Island, during the 12.4 kyr (kiloyear) since local deglaciation. We characterized OC endmembers and downcore sediment mixtures using Ramped Pyrolysis/Oxidation (RPO), radiocarbon (14C) age offsets between bulk sediment and macrofossils, and stable carbon isotopes (δ13C). We modeled endmember contributions to the lake sediment using the Bayesian mixing framework, MixSIAR. RPO revealed similar patterns between OC volatilization and pyrolysis temperature indicating minimal OC degradation between source and sink. Endmember OC accumulation rates, accounting for MixSIAR results, sedimentation, and total OC content, showed that mean postglacial soil inputs to Lake CF8 were greatest between 11.9 and 9.0 ka, 1.5 times greater than the rest of the record. This period coincided with regional peak Holocene summer temperatures (up to 5 °C (celsius) warmer than the pre industrial average), despite having low 14C age-offsets. Since modern Arctic temperatures have already warmed by 2-3 °C, similar to the HTM, regional permafrost may be mobilized at the same rates that we estimate for the early Holocene. 

Lacustrine δ2H and δ18O isotope proxies are powerful tools for reconstructing past climate and precipitation changes in the Arctic. However, robust paleoclimate record interpretations depend on site-specific lake water isotope systematics, which are poorly described in the eastern Canadian Arctic due to insufficient modern lake water isotope data. We use modern lake water isotopes (δ18O and δ2H) collected between 1994-1997 and 2017–2021 from a transect of sites spanning a Québec-to-Ellesmere Island gradient to evaluate the effects of inflow seasonality and evaporative enrichment on the δ2H and δ18O composition of lake water. Four lakes near Iqaluit, Nunavut sampled biweekly through three ice-free seasons reflect mean annual precipitation isotopes with slight evaporative enrichment. In a 23° latitudinal transect of 181 lakes, through-flowing lake water δ2H and δ18O fall along local meteoric water lines. Despite variability within each region, we observe a latitudinal pattern: southern lakes reflect mean annual precipitation isotopes, whereas northern lakes reflect summer-biased precipitation isotopes. This pattern suggests that northern lakes are more fully flushed with summer precipitation, and we hypothesize that this occurs because the ratio of runoff to precipitation increases with latitude as vegetation cover decreases. Therefore, proxy records from through-flowing lakes in this region should reflect precipitation isotopes with minimal influence of evaporation, but vegetation changes in lake catchments across a latitudinal transect and through geologic time may influence the seasonality of lake water isotopic compositions. Thus, we recommend that future lake water isotope proxy records are considered in context with temperature and ecological proxy records. 

Sedimentary plant wax δ 2H values are common proxies for hydrology, a poorly constrained variable in the Arctic. However, it can be difficult to distinguish plant waxes derived from aquatic versus terrestrial plants, causing uncertainty in climate interpretations. We test the hypothesis that Arctic lake sediment mid- and long-chain plant waxes derive from aquatic and terrestrial plants, respectively. We compare n-alkanoic acid and n-alkane chain-length distributions and n-alkanoic acid δ2H and δ13C values of the 29 most abundant modern plant taxa to those for soils, water filtrates, and lake sediments in the Qaupat Lake (QPT) catchment, Nunavut, Canada. Chain length distributions are variable among terrestrial plants, but similar and dominated by mid-chain waxes among submerged/floating aquatic plants. Sedimentary wax distributions are similar to those in submerged/floating aquatic plants and to Salix spp., which are among the most abundant terrestrial plants in the QPT catchment. Mid-chain n-alkanoic acid δ2H values are similar in sediments and submerged/ floating aquatic plants, but 50‰ lower than Salix spp. In contrast, sedimentary long-chain n-alkanoic acid δ2H values fall between those for submerged/floating aquatic plants and Salix spp. We therefore infer that mid-chain waxes in QPT are primarily from aquatic plants, whereas long-chain waxes are from a mix of terrestrial and aquatic plants. In Arctic lakes like QPT, terrestrial wax transport via leaf litter and surface flow is limited by low-lying topography and sparse vegetation. If these lakes also have abundant aquatic plants growing near the sediment-water interface, the aquatic plants can contribute large portions of sedimentary waxes. 

Paleo water isotope records can elucidate how the Arctic water cycle responded to past climate changes. We analyze the hydrogen isotope composition (δ2H) of plant‐derived n‐alkanoic acids (waxes) from Lake Qaupat, Baffin Island, Nunavut, Canada, to assess moisture sources and seasonality during the past 5.8 kiloannum (ka). We compare this record to a sedimentary ancient DNA (sedaDNA)‐inferred vascular plant record from the same lake, aiming to overcome the uncertainty of plant community impacts on leaf waxes. As the sedaDNA record reveals a stable plant community after the colonization of Betula sp. at 6.1 ka, we interpret plant wax δ2H values to reflect climate, specifically mean annual precipitation δ2H. However, the distributions of n‐alkanoic acid homologs suggest that aquatic mosses, which are not represented in the sedaDNA record, may become more abundant towards the present. Therefore, we cannot exclude the possibility that changes in the plant community cause changes in the plant wax δ2H record, particularly long‐chain waxes, which become less abundant through this record. We find that Lake Qaupat mid‐chain plant wax δ2H is enriched coincident with high Labrador Sea summer surface temperature, which suggests that local moisture sources in summer and early autumn have the greatest impact on precipitation isotopes in this region. 

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 kiloannum (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. 

Paleo water isotope records can elucidate how the Arctic water cycle responded to past climate changes. We analyze the hydrogen isotope composition (δ2H) of plant‐derived n‐alkanoic acids (waxes) from Lake Qaupat, Baffin Island, Nunavut, Canada, to assess moisture sources and seasonality during the past 5.8 ka. We compare this record to a sedimentary ancient DNA (sedaDNA)‐inferred vascular plant record from the same lake, aiming to overcome the uncertainty of plant community impacts on leaf waxes. As the sedaDNA record reveals a stable plant community after the colonization of Betula sp. at 6.1 ka, we interpret plant wax δ2H values to reflect climate, specifically mean annual precipitation δ2H. However, the distributions of n‐alkanoic acid homologs suggest that aquatic mosses, which are not represented in the sedaDNA record, may become more abundant towards the present. Therefore, we cannot exclude the possibility that changes in the plant community cause changes in the plant wax δ2H record, particularly long‐chain waxes, which become less abundant through this record. We find that Lake Qaupat mid‐chain plant wax δ2H is enriched coincident with high Labrador Sea summer surface temperature, which suggests that local moisture sources in summer and early autumn have the greatest impact on precipitation isotopes in this region.