RESULTS

The concentration profiles (in milligram per gram dry weight) of C_org and TN are presented in Figure F2. On average, elevated OM concentrations (C_org and TN) are apparent in the uppermost 2 m of the core (60.9 ± 14.8 and 5.4 ± 1.4 mg/gdw, respectively). From 200 to 270 cmbsf, C_org and TN concentrations show a marked minimum (41.5 ± 5.9 and 3.0 ± 0.6 mg/gdw, respectively). Further fluctuations between 40 and 70 mg/gdw for C_org and 2–5 mg/gdw for TN occur downcore during the early part of the Holocene. Organic matter concentrations stabilize at lower levels during the Pleistocene with averages for C_org and TN being 34.1 ± 6.9 and 2.4 ± 0.4 mg/gdw, respectively. These values are consistent with prior work in cores from the region that show C_org fluctuations, over the late Pleistocene to early Holocene, in the same range as those presented here (30–120 mg/gdw for ODP Hole 680B), with maximum concentrations in the most recent part of the Holocene (Wefer et al., 1990). The atomic C_org to TN ratio (C/N) increases continuously down through the Holocene from an initial value of 11–12 in recent sediments at the sediment/water interface to values that reach 14–15 at the base of the Holocene. The C/N ratio shows a further rapid increase across the Holocene/Pleistocene boundary (~380 cmbsf) and stabilizes around 17 ± 1 for the remainder of the core (Fig. F3).

The stable isotopic signatures of organic carbon (¹³C_org) from Hole 1229E cover a range of values from less ¹³C-depleted signatures (–18.5) to more strongly ¹³C-depleted samples (–22.5) (Fig. F3). The latest Holocene section of the core (uppermost 2 m) is characterized by overall intermediate carbon isotope values (–20.4 ± 1.1) with one interval characterized by a more ¹³C-depleted signature of –22.5. The section between 150 and 250 cmbsf is characterized by OM more depleted in ¹³C (–21.9 ± 0.4). Below follows an interval (270 and 370 cmbsf) with heavier ¹³C signatures (–20.4 ± 0.8) during the early Holocene. The carbon isotopic signatures remain relatively constant at –21.5 ± 0.4 during the Pleistocene.

All sediment samples from Hole 1229E yielded lignin-derived oxidation byproducts, albeit in trace amounts (total range = 2–30 µg/gdw). Total lignin phenol concentrations (sum of eight lignin-derived phenols [8] in micrograms per gram dry weight) (Hedges and Ertel, 1982) show variable levels throughout the core depth. Concentrations reach maxima in the uppermost meter of the core (15–30 µg/gdw), between 200 and 250 cmbsf (15 µg/gdw), and below 350 cmbsf (15 µg/gdw) (Fig. F4). Intervals of minimal lignin concentrations are observed between 100–200 and 250–350 cmbsf (range = 2–5 µg/gdw). Carbon-normalized lignin yields (sum of eight lignin-derived phenols normalized to carbon content [8] in micrograms per 100 mg C_org) (Hedges and Ertel, 1982) show a similar pattern. Surface (0–100 cmbsf) and midcore values (200–250 cmbsf) peak at 30–50 µg/100 mg C_org, whereas sediment intervals in the middle part of the Holocene (100–200 cmbsf) are characterized by low lignin yields (5–15 µg/100 mg C_org). There is no apparent relationship between the fluctuations in lignin and C_org concentrations, but there seems to be a weak correlation between carbon-normalized lignin yields and isotopic signatures (see "Discussion," below).