Authors:	Homann, Julia
Title:	Method development for the analysis of biochemical and paleo-environmental markers in speleothems
Online publication date:	8-Nov-2023
Year of first publication:	2023
Language:	english
Abstract:	Climate archives like speleothems, ice cores, sediment cores, or tree rings hold valuable information about local and global climatic events. They can be used to reconstruct different aspects of past environments and thus in turn help to predict future climate change. Speleothems are ideally suited as climate archives since they can grow continuously over a period of up to 100,000 years and their age can be determined absolutely with high accuracy and high resolution using U-series methods. Established proxies (e.g. isotopic ratios or trace elements) are increasingly complemented by organic biomarkers that record more specific aspects of paleoenvironmental conditions like vegetation type, fire dynamics, and temperature. The aim of this work was to develop trace analysis methods for three different groups of biochemical proxies in speleothems. The methods were then applied to real samples to elucidate temporal changes in the proxy signals and interpret them in regards to changes in the climatic and environmental conditions. In the first part of this work, an electrochemical method for the anodic oxidation and subsequent degradation of lignin in speleothems was developed to utilise the resulting lignin oxidation products (LOPs) as paleo-vegetation markers. LOPs were analysed using an ultra-high performance liquid chromatography system coupled to a high-resolution mass spectrometer. The method achieved comparable or even higher LOP concentrations than established CuO and CuSO4 oxidation methods. The method represents a new tool for the analysis and reconstruction of paleo-vegetation and has the potential to be applied to other climate archives and matrices. In the second part, levoglucosan, a combustion-sensitive anhydrosugar, and LOPs were analysed in a stalagmite, reconstructing fire activity and vegetation composition in the California Coast Range across the 8.2 kyr event. Elevated levoglucosan concentrations suggest increased fire activity while altered LOP compositions indicate a shift toward more woody vegetation during the event. These changes are concurrent with increased hydroclimate volatility as shown by carbon and calcium isotope proxies. Together, these records suggest that climate whiplash (oscillations between extreme wetness and aridity) and fire activity in California, both projected to increase with anthropogenic climate change, were tightly coupled during the early Holocene. In the last part, a sequential extraction of pulverised carbonate samples was conducted to analyse them for 16 polycyclic aromatic hydrocarbons (PAHs) and three monosaccharide anhydrides (MAs). The preparation method requires only small sample sizes; PAHs and MAs were measured by GC-MS and LC-HILIC-MS, respectively. The method was applied to 10 samples from a ~400-year-old stalagmite from Cenote Ch'en Mul, at Mayapan, the largest Postclassic Maya capital of the Yucatán Peninsula. A strong correlation between the major MA (levoglucosan) and non-alkylated PAHs (Σ15) was observed. Multiple diagnostic PAH and MA ratios were investigated and although not all were applicable as paleo-fire proxies, ratios that combine PAHs with MAs appear to be promising tools for identifying different fire regimes and inferring the type of fuel burned. In the 1950s and 1960s, levoglucosan and Σ15 concentrations roughly doubled compared to other times in the last 400 years, suggesting greater fire activity at Mayapan during these two decades. The higher concentrations of fire markers may be due to land clearance at the site and explorations of the cave by Carnegie Institution archaeologists.
DDC:	540 Chemie 540 Chemistry and allied sciences 550 Geowissenschaften 550 Earth sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 09 Chemie, Pharmazie u. Geowissensch.
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-9575
URN:	urn:nbn:de:hebis:77-openscience-e3ee76b4-4b58-4e99-a96b-3ecc6d266b7b4
Version:	Original work
Publication type:	Dissertation
License:	CC BY
Information on rights of use:	https://creativecommons.org/licenses/by/4.0/
Extent:	VII, 145 Seiten ; Illustrationen, Diagramme
Appears in collections:	JGU-Publikationen