Biomarker and Stable Isotopes of Plants, Soils, and Waters from a Northern Alaska Transect for Paleoclimate Calibrations

Climate change is predicted to be faster and more severe in high latitude regions than elsewhere globally due to positive feedback cycles. Increased understanding of the vegetation and soil microbial communities across modern biome boundaries will aid Paleoclimate reconstructions from high latitude environment. Biomarkers from modern plants and soils are potential tools that can be used to enhance understanding of these unique systems. Investigations of n-alkyl compounds from plants can be compared to soils to enhance understanding of early-diagenetic processes due to their ubiquity, resistance to degradation, and chemical inertness. Based on similarities in n-alkyl distributions from vegetation, we can determine a strong vegetation signal in soils, which aids in constraining paleoclimate models. Additionally, based on ratios of mid to long chain lengths from n-alkanoic acids it appears that mosses have a strong control on plant waxes in soils.

Hydrogen isotopes from n-alkyl lipids can also be used to look at hydroclimate variability. Water can leave an isotopic ‘fingerprint’ of paleoprecipitation in leaf waxes that can be preserved for millions of years. By looking at the major fractionations that occur from evaporation, transpiration, and biosynthesis, we can calculate an apparent fractionation (_wax/MAP) factor that can be used in paleoprecipitation estimates. We find this value to be similar using both n-alkanes and n-alkanoic acids, which are significantly more positive than commonly used values based largely on temperature vegetation. These results contribute to our growing understanding of plant water-wax fractionation in the high latitudes.

Microbial lipids from soils are often used in proxies used in paleoclimate reconstructions. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) and bacteriohopanepolyols (BHPs) are microbial membrane lipids that have been shown to alter based on environmental factors. Low-temperature soils collected along a transect of northern Alaska aided in calibrating commonly used paleoproxies based on brGDGTs. This work also provided the first proxies for pH, mean annual temperature and precipitation using BHPs, which were found to provide comparable results to ones based on brGDGTs. Overall, these results opened a wide range of opportunities for microbial and plant proxies to be applied in paleoclimate reconstructions from lesser studied high latitude environments.