Abstract
Abstract. Englacial ice contains a significant reservoir of organic material (OM), preserving a chronological record of materials from Earth's past. Here, we investigate if OM composition surveys in ice core research can provide paleoecological information on the dynamic nature of our Earth through time. Temporal trends in OM composition from the early Holocene extending back to the Last Glacial Maximum (LGM) of the West Antarctic Ice Sheet Divide (WD) ice core were measured by fluorescence spectroscopy. Multivariate parallel factor (PARAFAC) analysis is widely used to isolate the chemical components that best describe the observed variation across three-dimensional fluorescence spectroscopy (excitation–emission matrices; EEMs) assays. Fluorescent OM markers identified by PARAFAC modeling of the EEMs from the LGM (27.0–18.0 kyr BP; before present 1950) through the last deglaciation (LD; 18.0–11.5 kyr BP), to the mid-Holocene (11.5–6.0 kyr BP) provided evidence of different types of fluorescent OM composition and origin in the WD ice core over 21.0 kyr. Low excitation–emission wavelength fluorescent PARAFAC component one (C1), associated with chemical species similar to simple lignin phenols was the greatest contributor throughout the ice core, suggesting a strong signature of terrestrial OM in all climate periods. The component two (C2) OM marker, encompassed distinct variability in the ice core describing chemical species similar to tannin- and phenylalanine-like material. Component three (C3), associated with humic-like terrestrial material further resistant to biodegradation, was only characteristic of the Holocene, suggesting that more complex organic polymers such as lignins or tannins may be an ecological marker of warmer climates. We suggest that fluorescent OM markers observed during the LGM were the result of greater continental dust loading of lignin precursor (monolignol) material in a drier climate, with lower marine influences when sea ice extent was higher and continents had more expansive tundra cover. As the climate warmed, the record of OM markers in the WD ice core changed, reflecting shifts in carbon productivity as a result of global ecosystem response.
Highlights
In addition to its water stable isotope content that provides a proxy record of past temperatures (Dansgaard et al, 1993), ice archives atmospheric information on trace gases like CO2 and CH4 encapsulated in air bubbles and chemical species trapped in the ice lattice
Since organic material (OM) is a complex mixture containing a broad range of molecules in potentially overlapping fluorescent regions, the application of parallel factor (PARAFAC) analysis was used to resolve the representative subset of samples into individual OM fluorescing components characterized by their Ex–Em maxima
The contributions of fluorescent OM markers represented by PARAFAC C1 were dominant throughout the Last Glacial Maximum (LGM), last deglaciation (LD), and the Holocene compared to C2 and C3, indicating a consistent record of OM with chemical species similar to monolignols over time
Summary
In addition to its water stable isotope content that provides a proxy record of past temperatures (Dansgaard et al, 1993), ice archives atmospheric information on trace gases like CO2 and CH4 encapsulated in air bubbles and chemical species trapped in the ice lattice. Numerous inorganic species trapped in ice have been used to reconstruct past chemical compositions of the atmosphere, its recent change in response to growing human activities, and its past natural variability (Legrand and Mayewski, 1997; Petit et al, 1999; Johnsen et al, 2001; Alley, 2002; Wolff et al, 2006; Jansen et al, 2007; Luthi et al, 2008). As reviewed by Legrand et al (2013), information on the load and composition of organic matter (OM) archived in deep ice is still very limited (Legrand et al, 2013). D’Andrilli et al.: A 21 000-year record of fluorescent organic matter markers
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