Improved end-member characterization of modern organic matter pools in the Ohrid Basin (Albania, Macedonia) and evaluation of new palaeoenvironmental proxies

Abstract

Abstract. We present elemental, lipid biomarker and compound-specific isotope (δ13C, δ2H) data for soils and leaf litter collected in the catchment of Lake Ohrid (Albania, Macedonia), as well as macrophytes, particulate organic matter and sediments from the lake itself. Lake Ohrid provides an outstanding archive of continental environmental change of at least 1.2 M years and the purpose of our study is to ground truth organic geochemical proxies that we developed in order to study past changes in the terrestrial biome. We show that soils dominate the lipid signal of the lake sediments rather than the vegetation or aquatic biomass, while compound-specific isotopes (δ13C, δ2H) determined for n-alkanoic acids confirm a dominant terrestrial source of organic matter to the lake. There is a strong imprint of suberin monomers on the composition of total lipid extracts and chain-length distributions of n-alkanoic acids, n-alcohols, ω-hydroxy acids and α,ω-dicarboxylic acids. Our end-member survey identifies that ratios of mid-chain length suberin-derived to long-chain length cuticular-derived alkyl compounds as well as their average chain length distributions can be used as new molecular proxies of organic matter sources to the lake. We tested these for the 8.2 ka event, a pronounced and widespread Holocene climate fluctuation. In SE Europe climate became drier and cooler in response to the event, as is clearly recognizable in the carbonate and organic carbon records of Lake Ohrid sediments. Our new proxies indicate biome modification in response to hydrological changes, identifying two phases of increased soil OM supply, first from topsoils and then from mineral soils. Our study demonstrates that geochemical fingerprinting of terrestrial OM should focus on the main lipid sources, rather than the living biomass. Both can exhibit climate-controlled variability, but are generally not identical.

Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 640 ka and present day

“…Leng et al, 1999). At Lake Ohrid, low TOC/TN ratios are a result of OM degradation and clay-bound ammonium supply from the catchment, such as observed in core Lz1120 from the southeastern corner of the lake (Holtvoeth et al, 2015). Good OM preservation, low oxygen availability, and overall poor mixing conditions could have favored sulfide formation, such as pyrite, in lithotype 1 sediments.…”

Sources of organic matter for bacteria in sediments of Lake Rotsee, Switzerland

“…Generally, TOC/TN ratios of higher terrestrial plants vary in the range of 14-23, whereas the ratio is about 6-7 for plankton (Mu ¨ller and Mathesius 1999) and 4-6 for bacteria (Gon ˜i and Hedges 1995). In addition, soil OM can have a wide range of TOC/TN ratios (5-10.7), which generally tend to be lower than those of the overlying vegetation (Gon ˜i et al 1998;Holtvoeth et al 2016). TOC/TN ratios in the core (Fig.…”