Mid- and long-chain leaf waxes and their δ2H signatures in modern plants and lake sediments from mid-latitude North America

Compound-specific δ2H composition of leaf-wax n-alkanes are increasingly being used to infer past hydroclimates. Mid- and long-chain n-alkanes in sedimentary archives (i.e., C23 and C29) are thought to derive from aquatic and terrestrial plants, respectively, and track the isotopic composition of either lake water or precipitation. Yet, the relationship between the δ2H composition of alkane C23 and that of lake water is not well constrained. Here, we investigated n-alkane contributions to sedimentary archives from both aquatic and terrestrial plants by analyzing their distributions and δ2H signatures in plants and lake sediments at 29 sites across mid-latitude North America. We find that both aquatic and terrestrial plants synthesize alkane C23 and that sedimentary C23 δ2H values parallel those of terrestrial plants and differ from those of aquatic plants. Our results indicate that across mid-latitude North America, and globally, both mid- and long-chain n-alkanes in lake sediments commonly derive from terrestrial higher plants and that the C23 alkane is not a reliable predictor of lake water δ2H. Moreover, angiosperms and gymnosperms exhibit similar εapp values between the δ2H of alkane C29 and mean annual precipitation. Therefore, vegetation shifts between angiosperms and gymnosperms do not strongly affect εapp between alkane C29 and MAP.