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doi:10.2204/iodp.proc.342.205.2017

Analysis

For the organic geochemical analysis of GDGTs, 79 sediment samples (45 samples from Site U1406 and 34 samples from Site U1411; Tables T1, T2) were collected. Samples were freeze-dried and then mechanically ground. From 10 to 20 g of sediment was taken for further analysis. The total lipid extract was obtained by the accelerated solvent extraction (ASE) technique using dichloromethane/methanol (9:1 [v/v]) with the following settings:

• Pressure = 1500 psi;
• Static = 5 min;
• Flush = 60%;
• Purge = 60 s; and
• Cycles = 3.

Subsequently, the extract was separated over an activated Al₂O₃ column into an apolar (hexane/dichloromethane; 9:1 [v/v]) and a polar (dichloromethane/methanol; 1:1 [v/v]) fraction. The polar fraction, prior to GDGT analysis, was dissolved in hexane–isopropanol (99:1 [v/v]) and filtered over a 0.4 µm polytetrafluoroethylene filter. GDGTs were analyzed using high-performance liquid chromatography–mass spectrometry (HPLC-MS) as described by Schouten et al. (2007). Briefly, an Agilent (Palo Alto, CA, USA) 1100 HPLC high-sensitivity mass-selective detector (MSD SL) was used. Compounds were separated using a Prevail cyano column (150 × 2.1 mm; 3 µm; Alltech, Deerfield, IL, USA) maintained at 30°C. GDGTs were eluted isocratically with 99% hexane and 1% isopropanol for 5 min, followed by a linear gradient to 98% hexane and 2% isopropanol at a flow rate of 0.2 mL/min. Detection was achieved using single-ion monitoring. Relative qualification of the compounds was achieved by manual integration of the peaks in the mass chromatograms in the Agilent ChemStation manager software.

The BIT index values were calculated as described by Hopmans et al. (2004):

The roman numerals refer to individual brGDGT structures as shown in Figure F1 (for details see Schouten et al., 2013).

The MI was calculated following the equation given by Zhang et al. (2011):

The %GDGT-0 index was calculated following the equation given by Sinninghe DamstЩ et al. (2012):

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