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2.2. Analytical procedure
The grain sizes of the samples were determined using a laser particle size analyzer (Mastersizer 2000, Malvern Instruments Ltd., Malvern, Worcestershire, UK). The particle sizes were 63 μm for sand. The relative error in the particle sizes of duplicate samples was less than 3% (n = 6).
Portions of the freeze-dried sediment samples were decalcified using 4 M hydrochloric Fusion glycoprotein (92-106) and subsequently rinsed with deionized water (3–4 times) before drying overnight at 60 °C. The resulting carbonate-free samples were then analyzed for total organic carbon (TOC) and total nitrogen (TN) in duplicate using a pelvis Vario EL‐III Elemental Analyzer, and the average values were reported (Hu et al., 2009). Replicate analyses of one sample (n = 6) provided a precision of ± 0.02 wt.% for TOC and ± 0.005 wt.% for TN. Stable carbon isotope analysis of the organic carbon was performed on the carbonate-free samples using a Thermo Deltaplus XL mass spectrometer operating in continuous flow mode, according to the procedure of Hu et al. (2009).