A review of organic geochemistry in Antarctica

Organic constituents of the McMurdo, Syowa and Vestfold Oases have been reviewed with the viewpoint of organic geochemistry. The concentrations of total organic carbon (TOC), extractable organic carbon with ethyl acetate, total nitrogen (TN), hydrocarbons, fatty acids, sterols, hydroxy acids and phenolic acids in lake and pond waters and sediments show a wide range of variation depending on the sampling depths and locations, reflecting probably the difference of the distribution and activity of organisms there, although the contents of the organic compounds studied are generally low. Normal, branched and unsaturated hydrocarbons and fatty acids are found in the water and sediment samples, but their compositions differ considerably among the lakes and ponds. SixΔ^5-stenols and three 5α-stanols are identified in the water and/or sediment samples. Surprisingly, 24-ethylcholesterol is the most dominant sterol, which must come from blue-green algae and green algae in the lakes and ponds. The C_/C_ sterol ratios are considerably high (>1), and are not good geochemical markers for the Antarctic environment as usual meaning. The dominance of p-hydroxybenzoic acid among the phenolic acids found along with the absence of syringic, p-coumaric and ferulic acids in water and sediment samples reflect the absence of vascular plants in the areas studied, and are believed to be an important indicator for the absence of vascular plants. The concentrations of TOC, TN, hydrocarbons and fatty acids in soils in the dry valley areas of the McMurdo Oasis are extremely low, reflecting that organic carbon sources are highly restricted there. However, very long-chain n-alkanoic acids extending to C_ are found, having a small even-carbon predominance, and comprising a large proportion of the fatty acids in soils. They apparently originate in the Beacon sandstone