Alkenones analyses
Freeze-dried sediment samples were extracted by an accelerated solvent
extraction system with DCM: methanol mixture (9:1, v/v). The total lipid
extraction was further separated into three fractions of increasing
polarity by silica gel columns eluting with hexane, DCM, and methanol
subsequently. The mid-polar fractions containing alkenones were analyzed
on a gas chromatography–flame ionization detection Agilent 7890N Series
instrument with mid-polarity column RTX-200 (105 m × 250 μm × 0.25 μm)
with the oven program described in Zheng et al. (2017).