After all tuffs and background sediments were freeze-dried, 30 ml mixed solution of dichloromethane and methanol (9:1, V/V) was added to each Teflon tube containing ca. 10 g sample. The total lipid extract was extracted ultrasonically (repeated 5 times) and dried with nitrogen. The GDGTs were separated from total lipids by eluting silica gel column with mixture of dichloromethane and methanol (1:1, V/V). The GDGTs fractions were filtered with 0.45 μm PTFE membrane and then transferred to 250 μl insert vial. The internal standard C46 GDGT was added before the GDGTs were analyzed using an Agilent 1200 series liquid chromatography connected to an Agilent 6460A triple-quadruple mass spectrometer.#ringstetra: the weighted average number of cyclopentane moieties for tetramethylated brGDGTs#ringspenta: the weighted average number of cyclopentane moieties for pentamethylated brGDGTs#rings_tetra=(Ib+2×Ic)/(Ia+Ib+Ic)#rings_penta=(IIb+IIb'+2×IIc+2×IIC')/(IIa+IIa'+IIb+IIb'+IIc+IIc' )Rings_(penta-hexa)=IIb+IIb'+IIc+IIc'+IIIb+IIIb'+IIIc+IIIc'