High abundance of algal 24-ethylcholesterol in Antarctic lake sediment

Abstract

Sterols are one of the most widely distributed group of organic compounds in the environment, ranging in geological age from Recent to Cretaceous, and are commonly found in soils and contemporary lake and marine sediments 1-11. The major sterols found in lake sediments are stenols, cholest-5-en-3β-ol (C27), 24-methylcholesta-5,22-dien-3β-ol (C28), 24-methylcholest-5-en-3β-ol (C28), 24-ethylcholesta-5,22-dien-3β-ol (C29) and 24-ethylcholest-5-en- 3β -ol (24-ethylcholesterol, C29) and stanols, 5α-cholestan-3β-ol (C27), 24-methyl-5α-cholestan- 3β-o1 (C28) and 24-ethyl-5α-cholestan-3β-ol (C 29) (refs. 5-8, 10, 11). C29 sterols are abundant in vascular plants, whereas C27 sterols are often dominant in plankton. Thus C29/C27 sterol ratios are believed to be indicators both of allochthonous and autochthonous contributions of organic matter for lakes and of terrigenous sources of organic matter in marine environments 5,7,8,10,11. In the Antarctic, vascular plants are only found in the Antarctic Peninsula12. Thus the sterol composition of Antarctic lake sediments is expected to be considerably different from those in the temperate and tropical zones. Here we report the first analyses of sterols in Antartic lake sediments, which are found to contain high abundances of 24-ethylcholesterol. Such sterols must arise from blue-green and green algae in lakes and surrounding soils. © 1982 Nature Publishing Group.