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The role of high latitude lakes in storing and processing terrestrial organic carbon export is not well understood. We analyzed a 2.7-meter (m) -long sedimentary record from Eight Mile Lake that extends back 15,700 years to evaluate connections between productivity, organic carbon accumulation and late Quaternary environmental change in central Alaska. We analyzed macrofossil radiocarbon, alongside physical and biogeochemical properties. This dataset includes data from 12 sediment cores collected across Eight Mile Lake. These cores span time frames of 1000 - 15,700 years. This dataset includes bulk physical data, organic matter abundance, biogenic silica abundance, particle size, geochronological information, magnetic susceptibility data and hyperspectral imagery. 

The earliest Native Americans have often been portrayed as either megafaunal specialists or generalist foragers, but this debate cannot be resolved by studying the faunal record alone. Stable isotope analysis directly reveals the foods consumed by individuals. We present multi-tissue isotope analyses of two Ancient Beringian infants from the Upward Sun River site (USR), Alaska (~11,500 years ago). Models of fetal bone turnover combined with seasonally-sensitive taxa show that the carbon and nitrogen isotope composition of USR infant bone collagen reflects maternal diets over the summer. Using comparative faunal isotope data, we demonstrate that although terrestrial sources dominated maternal diets, salmon was also important, supported by carbon isotope analysis of essential amino acids and bone bioapatite. Tooth enamel samples indicate increased salmon use between spring and summer. Our results do not support either strictly megafaunal specialists or generalized foragers but indicate that Ancient Beringian diets were complex and seasonally structured. 

Abstract Sub‐centennial oxygen (δ¹⁸O) isotopes of ostracod and authigenic calcite from Squanga Lake provides evidence of hydroclimatic extremes and a series of post‐glacial climate system reorganizations for the interior region of northwest Canada. Authigenic calciteδ¹⁸O values range from −16‰ to −21‰ and are presently similar to modern lake water and annual precipitation values. Ostracodδ¹⁸O record near identical trends with calcite, offset by +1.7 ± 0.6‰. At 11 ka BP (kaBP = thousands of years before 1950), higherδ¹⁸O values reflect decreased precipitation−evaporation (P−E) balance from residual ice sheet influences on moisture availability. A trend to lowerδ¹⁸O values until ∼8 ka BP reflects a shift to wetter conditions, and reorganization of atmospheric circulation. The last millennium and modern era are relatively dry, though not as dry as the early Holocene extreme. North Pacific climate dynamics remained an important driver of P−E balance in northwest Canada throughout the Holocene. 

Abstract Vegetation greenness has increased across much of the global land surface over recent decades. This trend is projected to continue—particularly in northern latitudes—but future greening may be constrained by nutrient availability needed for plant carbon (C) assimilation in response to CO₂enrichment (eCO₂). eCO₂impacts foliar chemistry and function, yet the relative strengths of these effects versus climate in driving patterns of vegetative greening remain uncertain. Here we combine satellite measurements of greening with a 135 year record of plant C and nitrogen (N) concentrations and stable isotope ratios (δ¹³C and δ¹⁵N) in the Northern Great Plains (NGP) of North America to examine N constraints on greening. We document significant greening over the past two decades with the highest proportional increases in net greening occurring in the dries and warmest areas. In contrast to the climate dependency of greening, we find spatially uniform increases in leaf‐level intercellular CO₂and intrinsic water use efficiency that track rising atmospheric CO₂. Despite large spatial variation in greening, we find sustained and climate‐independent declines in foliar N over the last century. Parallel declines in foliar δ¹⁵N and increases in C:N ratios point to diminished N availability as the likely cause. The simultaneous increase in greening and decline in foliar N across our study area points to increased N use efficiency (NUE) over the last two decades. However, our results suggest that plant NUE responses are likely insufficient to sustain observed greening trends in NGP grasslands in the future.