Application of quantitative methods for microbial biomass, community structure, and nutritional status to the subsurface samples collected with careful attention to contamination reveals the presence of a group of microbes. The microbiota is sparse by several measures of biomass compared with that present in surface sediments and soils. The community structure, as characterized by the patterns of ester-linked fatty acids from the phospholipids, shows an absence of long-chain polyenoic fatty acids typical of microeukaryotes and high proportions of fatty acids typical of bacteria. Subsurface samples contain a higher proportion of glycerol teichoic acids than surface samples. Microbes in uncontaminated subsurface sediments show nutritional stress as evidenced by high levels of poly-β-hydroxybutyrate and extracellular polysaccharides. The proportions of ester-linked phospholipid fatty acids show distinctive differences between surface and subsurface, between subsurface sandy clay and limestone, and between two sites of subsurface sandy clay as shown using stepwise discriminant analysis. Contamination increased the microbial biomass, shifted the community to a more gram-negative bacterial consortium, and induced growth as evidenced by phospholipid fatty acid biosynthesis.

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The lipid composition of natural populations of diatoms in the sea ice at McMurdo Sound was determined during the austral spring bloom of 1985, using and Iatroscan TLC–FID system. The major lipid classes in all samples were polar lipids (including phospholipid, glycolipid and chlorophyll) and triacylglycerol, with lesser proportions of free fatty acids. Total lipid increased through November and early December, reaching a maximum (3300 mg m−2 at Cape Armitage and 1800 mg m−2 at Erebus Ice Tongue) c. one week after the chlorophyll a maxima. This increase was largely attributable to a corresponding increase in triacylglycerol. At the lipid maxima, triacylglycerol/polar lipid ratios in the range 1.0 to 2.5 were observed. The dynamic variations in lipid class abundances indicate that profound changes in the physiology of sea-ice diatoms are occurring throughout the spring bloom. A range of sterols (C26–C30) were detected; 24-methylenecholesterol, brassicasterol and 24-ethylcholesterol were the major sterols at the Cape Armitage and Erebus sites. The similarity of the sterol profiles to those of Antarctic freshwater algal communities strongly indicates diatoms as a more probable source of C29 sterols in the freshwater lakes than cyanobacteria or other algal groups. The hydrocarbons isolated from sea-ice diatoms at all sites were dominated by two unsaturated components, n−C21:6 and a diunsaturated isoprenoid C25 alkene. Until this study, no biological source had been validated for the isoprenoid C25:2 diene, even though it has been detected in many estuarine and coastal sediments.

Signature lipids from the phospholipid esterlinked fatty acids (PELFA) of cell membranes were used to describe benthic microbial communities of 4 Antarctic sediments. Metabolic activities of the communities were determined by incorporation of [3H]thymidine into bacterial DNA and sodium [14C]acetate into membrane lipids. Biomass measurements from extractable phospholipid fatty acids per g dry wt. ranged between 6 to 76 nmol, or when converted to number of bacteria, 3.7 × 108 to 4.5 × 109 cells per g dry wt. The West Sound site at New Harbor contained the lowest biomass, while Cape Evans on the East Sound contained the greatest. A marked difference was also noted between sites in their sediment microbial community structure. The East Sound sites at Cape Armitage and Cape Evans contained a greater abundance of diatom marker lipids, whilst both sides of the Sound contained approximately the same relative amounts of bacterial groups distinguished using PELFA. Activity of sediment microorganisms measured by radiolabel incorporation under ambient conditions followed the trends of the biomass measurements. The East Sound sites were more active by an average of 45–73% for [3H]thymidine and possibly also for sodium [14C]acetate.

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