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doi:10.2204/iodp.proc.336.203.2015

Results

Sediments

TC contents range from 6 to ~11 wt% for whole-sediment samples. Depth profiles of TC were similar at the three sites (Holes U1382B, U1383D, and U1384A) (Table T1; Fig. F2). These values were consistent with TC data for North Pond sediments reported by Bode (1979). From 0 to ~40 mbsf, TC increases with depth, with maximum values at approximately 20–40 mbsf. From 40 to ~90 mbsf, TC decreases with depth. δ¹³C-TC ranges from –0.04‰ to about +1.93‰ for whole-sediment samples (Table T1; Fig. F2). Both δ¹³C-TC values and TC contents change at a certain depth (Table T1; Fig. F2).

Basalts

TC (approximately 0.01–0.37 wt%) and total organic carbon (TOC) (approximately 0.01–0.03 wt%) values of basalts are almost constant over the depth interval analyzed (Table T2; Fig. F3), whereas sediment breccias and carbonates contain more carbon than basalts (approximately 3.56–11.9 wt%). The carbon isotopic composition of TC (δ¹³C-TC) of basalt samples ranges approximately from –21.8‰ to +2.69‰. Sediment breccias and carbonates have slightly higher δ¹³C-TC, at approximately –18.6‰ to +2.82‰. The carbon isotopic compositions of TOC (δ¹³C-TOC) of the corresponding samples show constant values (approximately –25‰) over the depth interval analyzed. The carbon isotopic compositions of kerogen (δ¹³C-kerogen) have slightly lower values (approximately –30.4‰ to –27.6‰) than those of δ¹³C-TOC (Table T2). In HCl/HF treatment, it is likely that the F^– ion forms fluoride as a secondary product (Cody et al., 2005), which might cause errors between δ¹³C-TOC and δ¹³C-kerogen. Our data are roughly comparable with δ¹³C-TOC for the Juan de Fuca basalts (approximately –34.6‰ to –21.6‰) (Lever et al., 2013). However, the carbon isotopic compositions of basalts probably show mass-dependent isotopic fractionation because the TC and TOC of basalts were low.

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