Hydrogen and carbon isotope fractionation in modern plant wax n-alkanes from the Falkland Islands
2022
Corcoran, Megan C. | Diefendorf, Aaron F. | Lowell, Thomas V. | Hall, Brenda L. | Spoth, Meghan M. | Schartman, Anna | Brickle, Paul
The hydrogen isotopic composition of terrestrial plant waxes (δ²Hwₐₓ) is widely used to reconstruct past hydroclimate. δ²Hwₐₓ values reflect plant source water or precipitation δ²H (δ²Hₚᵣₑcᵢₚ) values, and when extracted from sediment archives, records of past δ²Hₚᵣₑcᵢₚ values can be generated. In order to better interpret these δ²Hwₐₓ records, modern calibrations between plant waxes and source water are required when vegetation and location diverge from plant calibrations in other regions. To date, no modern study has examined how δ²Hwₐₓ values and source water δ²H values relate in the southern mid- and high-latitude maritime climatic regions where the climate is affected by the Southern Hemisphere Westerly Wind Belt. We present the first modern calibration of δ²Hwₐₓ values on the Falkland Islands by analyzing n-alkane plant wax concentrations, δ²H and δ¹³C values from 11 of the most common plant species, one lichen species, and surface lake sediment samples from four sites on Mount Usborne on East Falkland. Based on plant wax concentrations, the most commonly observed plants on the landscape, Empetrum rubrum and Cortaderia pilosa, are contributing the most to the waxes in sediment archives. We calculate the fractionation between the n-C₂₉ alkane δ²Hwₐₓ and δ²Hₚᵣₑcᵢₚ values (ε²Hwₐₓ/ₚᵣₑcᵢₚ) for all plant species to be –110 ± 17‰ (1σ, n = 22), which is similar to the global average ε²Hwₐₓ/ₚᵣₑcᵢₚ. Observed and modelled monthly δ²Hₚᵣₑcᵢₚ values indicate that δ²Hwₐₓ values can be interpreted as mean annual δ²Hₚᵣₑcᵢₚ values, ultimately establishing the framework for utilizing plant wax-based paleoreconstructions from the mid-latitude maritime climatic regions.
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