Lignin oxidation products in soil, dripwater and speleothems from four different sites in New Zealand

Heidke, Inken; Hartland, Adam; Scholz, Denis; Pearson, Andrew; Hellstrom, John; Breitenbach, Sebastian F. M.; Hoffmann, Thorsten

Lignin oxidation products (LOPs) are widely used as vegetation proxies in climate archives, such as sediment and peat cores. The total LOP concentration, inline-formulaΣ8, provides information on the abundance of vegetation, while the ratios inline-formula M2inlinescrollmathml chem normal C / normal V 23pt14ptsvg-formulamathimg033934f74fa8012bb4f0f71877bb007f bg-18-2289-2021-ie00001.svg23pt14ptbg-18-2289-2021-ie00001.png and inline-formula M3inlinescrollmathml chem normal S / normal V 23pt14ptsvg-formulamathimgcf64cc3a04b8b159572403b8c5f3628a bg-18-2289-2021-ie00002.svg23pt14ptbg-18-2289-2021-ie00002.png of the different LOP groups also provide information on the type of vegetation. Recently, LOP analysis has been successfully applied to speleothem archives. However, there are many open questions concerning the transport and microbial degradation of LOPs on their way from the soil into the cave system. These processes could potentially alter the original source-dependent LOP signals, in particular the inline-formula M4inlinescrollmathml chem normal C / normal V 23pt14ptsvg-formulamathimg247ad4fada0ef54c08c9d3f8e66647b1 bg-18-2289-2021-ie00003.svg23pt14ptbg-18-2289-2021-ie00003.png and inline-formula M5inlinescrollmathml chem normal S / normal V 23pt14ptsvg-formulamathimg4a2498c5458b18f9d6895a66b0950591 bg-18-2289-2021-ie00004.svg23pt14ptbg-18-2289-2021-ie00004.png ratios, and thus complicate their interpretation in terms of past vegetation changes. We analyzed LOPs in leaf litter and different soil horizons as well as dripwater and flowstone samples from four different cave sites from different vegetation zones in New Zealand using ultrahigh-performance liquid chromatography coupled to high-resolution mass spectrometry. We test whether the original source-dependent LOP signal of the overlying vegetation is preserved and can be recovered from flowstone samples and investigate how the signal is altered by the transport from the soil to the cave. The LOP concentrations range from mg ginline-formula−1 in the soil to ng ginline-formula−1 in the flowstones. Our results demonstrate that, from the soil to the flowstone, the inline-formula M8inlinescrollmathml chem normal C / normal V 23pt14ptsvg-formulamathimg2cbaf1659d77d79f730a75e99cbe2377 bg-18-2289-2021-ie00005.svg23pt14ptbg-18-2289-2021-ie00005.png and inline-formula M9inlinescrollmathml chem normal S / normal V 23pt14ptsvg-formulamathimgda8962b8ea93e4dd9eeb2c51d6478db2 bg-18-2289-2021-ie00006.svg23pt14ptbg-18-2289-2021-ie00006.png ratios both increase, while the total lignin content, inline-formulaΣ8, strongly decreases. This shows that the LOP signal is strongly influenced by both transport and degradation processes. Nevertheless, the relative LOP signal from the overlying soil at the different cave sites is preserved in the flowstone. We emphasize that for the interpretation of inline-formula M11inlinescrollmathml chem normal C / normal V 23pt14ptsvg-formulamathimgbc8a25506874e426825732ad6a340bea bg-18-2289-2021-ie00007.svg23pt14ptbg-18-2289-2021-ie00007.png and inline-formula M12inlinescrollmathml chem normal S / normal V 23pt14ptsvg-formulamathimg6c25f0c303e4bca03b5451c734e9c519 bg-18-2289-2021-ie00008.svg23pt14ptbg-18-2289-2021-ie00008.png ratios in terms of past vegetation changes, it is important to compare only samples of the same type (e.g., speleothem, dripwater or soil) and to evaluate only relative variations.

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Heidke, Inken / Hartland, Adam / Scholz, Denis / et al: Lignin oxidation products in soil, dripwater and speleothems from four different sites in New Zealand. 2021. Copernicus Publications.

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