LEAF WAXES AS CLIMATE PROXIES IN HIGH LATITUDE AND HIGH ALTITUDE LAKES

The use of biomarkers as climate proxies has expanded dramatically in the past decade, but thus far biomarkers have been applied mainly in the ocean and in lakes at low- to mid-latitudes. We present an overview of leaf waxes as climate proxies on the Tibetan Plateau and in the Arctic, regions that respond sensitively to climate change, with profound societal and ecological impacts. Leaf waxes are long chain hydrocarbon compounds produced as protective coatings by plants. Leaf wax abundance, chain length, and isotopic composition (δ²H, δ¹³C) change in response to climate and plant ecology. We will discuss our work developing and using leaf waxes as climate proxies in lakes on the northern Tibetan Plateau and in the Baffin Bay region in the Arctic. In each region, we first compare sub-decadal resolution records of leaf wax δ²H (δ²H_wax) to instrumental data to assess the response of these proxies to recent climate variability, and then we produce sub-millennial-resolution Late Pleistocene-Holocene records of δ²H_wax and δ¹³C_wax.

On the northern Tibetan Plateau where potential evapotranspiration is high (~2000 mm/yr), δ²H_wax responds to spring precipitation-evaporation balance (P-E). δ²H_wax is depleted when P-E is more negative, indicating that plants may use a source of depleted isotopes (e.g., groundwater, snowmelt) for biosynthesis when there is more evaporation. δ²H_wax and δ¹³C_wax records from Lake Qinghai show that the Tibetan Plateau was extremely dry and experienced dramatic shifts in plant communities during Heinrich Event 1 and the Younger Dryas.

In the Arctic, δ²H_wax likely responds to summer temperature: δ²H_wax is depleted when summer temperature is low (Thomas et al., 2012). In Disko Bay, Greenland, we are generating a centennial-scale Holocene temperature record using δ²H_wax. The chain length distribution also changes throughout the record. Using chain length distributions of modern plants from the lake’s catchment as analogs, we infer that the landscape was dominated by herbs immediately following deglaciation at 8.0 ka, and colonized by shrubs and grasses by 7.5 ka.