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doi:10.2204/iodp.proc.323.203.2016

Results

Carbon and oxygen stable isotope records derived from the benthic foraminifers at Site U1344 are shown in Figures F1 and F2. Data are provided in Table T1.

Abundance of benthic foraminifers at Site U1344 drops significantly downhole with no single species occurring continuously throughout the record. Noticeably, Uvigerina, which is relatively abundant in the upper 270 m CCSF-A of the stratigraphic section, is absent from all examined samples below that depth to the base of the record (~1.9 Ma) (see the “Site U1344” chapter [Expedition 323 Scientists, 2011b]). In samples where neither U. senticosa nor E. batialis are present, specimens of V. sadonica, G. pacifica, or N. labradorica were picked and analyzed. Analysis of different benthic foraminifer species allowed us to compare the stable isotopic composition of these species (Fig. F2) and infer their microhabitat preferences. Previous studies show a direct correlation between microhabitat depth within the sediment and the δ¹³C composition of benthic foraminifers (McCorckle et al., 1990; Ravelo and Hillaire-Marcel, 2007). Deep-dwelling infaunal species are generally isotopically lighter than species living at the sediment/water interface. Figure F2 shows the relationship between the δ¹⁸O and δ¹³C composition of U. senticosa, E. batialis, V. sadonica, G. pacifica, and N. labradorica. Of these, U. senticosa exhibits the highest and most narrow range of δ¹³C values of the four species (approximately –1.0‰), whereas E. batialis shows the lightest values (average = –2.9‰) and widest δ¹³C range. Both Uvigerina spp. and E. batialis are known as shallow infaunal species (e.g., Bubenshchikova et al., 2008; Asahi et al., in press), whereas V. sadonica and G. pacifica are considered intermediate infaunal species (Bubenshchikova et al., 2008). However, the lightest δ¹³C values in E. batialis found at Site U1344 suggest that this species may live deeper in the sediment than previously known or may preferentially feed on more degraded organic matter such as phytodetritus.

The correlation of the Site U1344 composite benthic δ¹⁸O record with the LR04 global stack curve (Lisiecki and Raymo, 2005) provides a high-resolution age model at Site U1344 for the last 140 ky. (Figs. F3, F4; Table T2). The interval of marine isotope Stages (MIS) 1–6 were identified on the composite δ¹⁸O record from the seafloor to 64 m CCSF-A (Fig. F4). The age-depth plot (Fig. F5) reveals high sedimentation rates with an average of ~46 cm/ky at Site U1344 over the last ~120 ky. During MIS 6 and 5e, relatively low sedimentation rates (~30 cm/ky) were observed (Fig. F5). Because of scarce δ¹⁸O data, the chronology during MIS 5d and 5e is ambiguous (Fig. F5).

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