Lignins

This is Earth Week, and chemists are celebrating the theme Glaciers: Hot Topic, Cool Chemistry!

As you might expect, glaciers contain all sorts of substances as the result of particles being entrapped in the ice. One of these substances is lignin, which Molecule of the Week first presented on June 25, 2012. Lignins are one of the most abundant natural aromatic polymers; they are major cell-wall components of wood and grasses.

Glaciers can be “fingerprinted” by identifying the types and amounts of organic substances found in them. In 2022 as an example, Yongqin Liu and collaborators at the Chinese Academy of Sciences (Beijing), Lanzhou University, the Chinese University of Petroleum (Beijing), and Xiamen University (all in China) examined the differences in dissolved organic matter (DOM) from lignins and other substances in the central and southern glaciers of the Tibetan Plateau.

Using ultra-high-resolution mass spectrometry, the authors found that there were no significant differences in DOM concentration or composition in snow and ice samples from the two glaciers. But cryoconite (windblown dust deposited in glaciers) from the southern glacier contained significantly higher relative intensities of lignins, carbohydrates, tannins, and other condensed aromatic compounds than the central glacier cryoconite. And DOM in the cryoconite on the central glacier came predominantly from lignin decomposition, whereas the southern glacier DOM did not. The authors attribute these differences to the higher forest cover and anthropogenic inputs from Indian monsoons in the southern glacier.

Lignins are important for glaciologists in other ways. Also in 2022, Petra Vinšová at Charles University (Prague) and colleagues there and in Switzerland, Canada, and the United States wrote that lignins and other organic substances in subglacial sediments from retreating glaciers are key to the early stages of formation of future glaciers.