Distribution of branched tetraether lipids in ponds from Inner Mongolia, NE China: Insight into the source of brGDGTs

We examined the distributions of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in surface sediments and associated catchment soils of 11 Inner Mongolian ponds (NE China) that collectively comprise a salinity gradient. We explored the sources of brGDGTs in the surface sediments, specifically the recently identified brGDGT isomers. Comparison of brGDGT distributions between surface sediments and soils indicated that the proportion of brGDGTs produced in situ within ponds was relatively minor compared with that contributed from catchment soils. The sole exception was the recently identified 6-Me hexamethylated brGDGT (IIIa′) isomer which, in the surface sediments, appeared to be significantly produced in situ or in the water column. However the 6-Me pentamethylated brGDGT (IIa′) isomer was derived primarily from the surrounding soils based on the plot of individual brGDGT isomers. By extension, the brGDGT-IIIa′ and -IIa′ components in surface sediments have different biological sources but in soils share a similar biological source.