Molecular and isotopic proxies

The Leaf Wax Lab

The Feakins Leaf Wax Lab focuses on compound specific carbon and hydrogen isotopic analyses of biomarkers for terrestrial vegetation. Biomarkers are molecules that can be attributed to a particular organism or group of organisms. We focus on biomarkers for terrestrial vegetation in particular the plant leaf waxes. These can be analyzed by gas chromatography isotope ratio mass spectrometry and are well preserved in the geological record. We seek to establish modern calibrations as well as apply these tools to paleoclimate reconstructions, deep in geological time.

Drought tolerance in crops

In collaboration with agricultural researchers we are translating plant wax biomarker and isotopic approaches to exploring the development of drought tolerance in agricultural crops and using agricultural field-experiment to test theories about plant wax function and climate response (Liu et al., 2017, 2019a, 2019b, Jiang et al., in review).

Grasslands

A current focus is modern soil surveys within grasslands, with transects across the Cerrado of Brazil (sampling by Christoph Haggi) and the Serengeti of Africa (sampling by Emily Beverly), in addition to the experimental work on crop grasslands summarized above (experimental work by Xiuwei Liu). We hope to calibrate the grassland ‘endmember’ on different continents and under different soil and climate conditions, in order to better understand the sedimentary signature of grasslands seen in our paleoecological reconstructions.

Tropical rainforests and cloud forests

Our lab has been deeply entrenched in a transect from the cloud forests of the high Andes down to the lowland tropical rainforest within Peru. We joined forces with the CHAMBASA project to generate an unprecedented leaf wax calibration study fully embedded in an ecological survey (Feakins et al., 2016a GCA, 2016b OG, Wu et al., 2017 GCA). We undertook soil surveys and river studies in the same region too (Ponton et al., 2014, Feng et al., 2016, Feakins et al., 2018 GCA, Wu et al., 2019 OG, Kirkels et al., 2020) to understand altitude effects in biomarkers how they are stored in soils and using those patterns to tag origins of biomarkers in fluvial transit towards understanding catchment sourcing.

Understanding transport pathways

A major unknown is in the pathway between plant and sediment. How does sourcing vary across landscapes and how do transport processes modulate the signals of past environments captured in sedimentary archives. We are working to understand these processes in the Andes in the Madre de Dios catchment using leaf wax hydrogen isotopes (Ponton et al., 2014), carbon isotopes, lignin (Feng et al., 2016), dual plant wax C and H isotopes (Feakins et al., 2018) and GDGTs (Kirkels et al., 2020), with radiocarbon insights of timescales of integration coming next (West et al., in prep.).

Proxy development: leaf wax hydrogen isotopes

The Feakins Leaf Wax Lab is located in subtropical, southern California. Bathed in sunshine but short on water, we have been developing the understanding of the hydrogen isotopic signals preserved in plant biomarkers, in arid regions (Feakins and Sessions, 2010a,b, Feakins et al., 2014), with a view to reconstructing climate variability and understanding arid environments . We then moved into the tropics (see Peruvian and Brazilian studies detailed above) to push forward our understanding of hydrogen isotope systematics there, see publications.

Hydrogen isotopes, past climates and the water cycle

Hydrogen isotopes in plant leaf waxes have the potential to record variations in water isotopes in the hydrological cycle, tracers ideal for tracking changes in global and regional circulation and the patterns of precipitation which are some of the most important aspects of climate change since water exerts strong feedbacks on the climate system and is essential for life. Leaf wax hydrogen isotope reconstructions of hydroclimate changes find global applications including Antarctica (Feakins et al., 2012, 2014), Africa (Feakins, 2013), California (Feakins et al., 2014, Feakins et al., 2019), Asia (Aichner et al., 2015, Sharifi et al., 2015, Aichner et al., 2019). see publications and press

Carbon isotopes and photosynthesis pathway

Carbon isotopes are a powerful tool to analyze plant photosynthetic strategies (C3, C4 and CAM) that are sensitive to climate change. Their changing proportion through time reveals insights into aridity, carbon dioxide levels in the atmosphere and temperature. In a recent paper we explore the leaf wax evidence for the expansion of the C4 pathway over 12 million years (Feakins et al., 2013). see publications and press

Carbon and hydrogen isotopes are particularly insightful in combination. As part of efforts to increase our understanding the hydrogen isotope signals preserved by plant leaf waxes, we are exploring the fundamentals of fractionation associated with different plant types, different environments and different metabolisms. For example we have demonstrated how CAM metabolism influences hydrogen isotope fractionation (Feakins and Sessions, 2010), and we analyzed plant type differences in a global dataset compiled from the published literature as part of a large community review (Sachse et al., 2012). Carbon and hydrogen isotopes together provide insights into climatic and vegetation changes. Paired C and H isotope reconstructions for NE Africa (Liddy et al., 2016), Indus (Liddy, 2017 PhD thesis) and Bengal Fan catchments are underway.