The development of novel terrestrial palaeoclimate proxies based on 3-hydroxy fatty acids

A wide range of environmental information from both terrestrial and marine realms is required from palaeoclimate archives to better understand the climate system and to provide a palaeoclimatic context for predictions of future rates of climate change, impact and Earth system sensitivity. Overall, far less attention has been paid to terrestrial environments, compared to the marine realm, due to the paucity of ubiquitous biomarkers with quantitative palaeoclimatic utility.
We have recently found strong correlations between 3-hydroxy fatty acid (3-OH-FA) distributions, synthesised within Gram-negative bacterial membranes, and environmental parameters (Wang et al., 2016). Based on this discovery we have defined new geochemical proxies for reconstructing temperature, pH and precipitation. The ubiquitous natural distribution of Gram-negative bacteria means that these new techniques for reconstructing past climate have huge potential.

We have recently submitted the first manuscript to demonstrate that 3-OH-FA biomarkers can successfully reconstruct temperature and precipitation signals from an individual stalagmite (Wang et al, submitted). This PhD project will undertake the next exciting steps in the development of these biomarkers:

- The production of new global scale calibrations to expand and refine the new proxies for pH and temperature and ensure wide uptake by the palaeoclimate community.
- First applications of new proxies to a variety of palaeoclimate archives beyond speleothems (lake sediments, ocean drilling sediment cores) on a variety of time-scales (Holocene to Cenozoic).

Methodology:
Geological work: Compile a collection of soil and sediment samples which span gradients in temperature, hydrology and a diversity of bacterial and plant communities. Fresh samples will be obtained on field expeditions from regional transects (in the USA and Europe). In addition we have already obtained samples from the ISRIC soil repository and co-supervisor Griffiths possesses a frozen archive of soils from across the UK collected as part of nationwide soil surveys, and a recent NERC funded project (U-GRASS) under the Soil Security Programme.

Experimental work: All samples will be subjected to organic geochemical extraction and clean-up and analytical methods: i.e. acid hydrolysis and digestion Wang et al., 2012), extraction with organic solvents, separation into chemical fractions and analysis by GC-FID, GC-MS.