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TEX 86 , calculated based on the distribution of isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs), is used worldwide for paleotemperature reconstruction in marine and lacustrine environments. Recently, however, increasing evidence showed that TEX 86 could be affected by multiple environmental variables. In this study, TEX 86 was calculated for core and polar GDGTs obtained from water column and surface sediments in the lower Pearl River and its estuary. Together with previously published core GDGT data from the coastal and open South China Sea (SCS), a comparison was made between TEX 86 -derived and satellite-based surface water temperature, which showed a TEX 86 -temperature minimum that is considerably lower than winter satellite temperature in the transitional zone between the Pearl River estuary and the coastal SCS. TEX 86 showed significantly positive correlation with GDGT-2 and GDGT-3 in this transitional zone, indicating that they are the primary compounds for the TEX 86 bias toward cooler temperature. Lipid and molecular DNA data both indicate that the variation in archaeal community composition rather than water depth or seasonality is likely the crucial factor causing the deviation of TEX 86 in the transitional area. Our study has implications for studies in ancient continental margins where unusually low TEX 86 temperatures may be observed in the geological record. [ABSTRACT FROM AUTHOR]