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  1. We compare hydrogen isotopic measurements of long-chain leaf-wax n-alkanes (2Hw; C27, C29, and C31) from Martin Lake, IN, United States of America (USA), with a calcite-based reconstruction of the oxygen isotopic composition of precipitation (18Op) from the same lake. We observe stable and high 2Hw during the Common Era (last 2000 years), which we interpret as growing-season precipitation originating mainly from the Gulf of Mexico and Atlantic. During the Little Ice Age (LIA; 1200-1850 CE), 2Hw values increased by 3-8 ‰, concomitant with a significant decrease in 18Op values by up to 12.5 ‰. Multiple proxy records for this time indicate persistent growing-season drought. We interpret these relatively high 2Hw values, as compared to the 18Op values, as a signal of low relative humidity that resulted in an 2H enrichment in plant source water resulting in high 2H values through enhanced plant water and/or soil evaporation. These results support the occurrence of low humidity conditions during the LIA in the midcontinental USA that also contributed to the marked decline of regional pre-Columbian Mississippian populations. 
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    Free, publicly-accessible full text available May 8, 2025
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  7. Rationale

    Plant lipid biomarkers, such as plant waxes and terpenoids, and the stable isotopic composition of bulk leaves are widely used in both modern and paleoclimate studies for tracking vegetation and climate. However, the effects of different drying methods on the preservation of plant lipid biomarkers and the stable isotopic compositions of leaves are less explored. Here, we investigated various drying methods for the measurement of plant lipid concentrations and bulk leaf isotopic compositions.

    Methods

    Leaves from four tree species (Acer rubrum,Pinus sylvestris,Platanus occidentalis, andTaxodium distichum) were collected and dried using air, an oven, a freeze‐dryer, and a microwave. We compared concentrations of leaf waxes and terpenoids and carbon (δ13C) and nitrogen (δ15N) isotopic compositions of leaves by different drying methods.

    Results

    The air, oven, freeze‐dryer, and microwave drying methods did not affect lipid concentrations significantly, and only a few homologues differed (38.1% or 41.8 μg/g on average) possibly due to biological variations or enhanced extraction efficiencies. The δ13C values were not affected by drying methods, whereas the δ15N values in oven‐dried leaves in some species were higher by 0.2–0.7‰ than those obtained by other methods. Though small, we attribute these patterns to loss of leaf compounds with lower isotope ratios during oven‐drying.

    Conclusions

    Based on our results, each drying technique yielded equivalent results for all plant wax and terpenoid concentrations and bulk leaf δ13C values; however, oven‐drying modified the δ15N values.

     
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