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doi:10.2204/iodp.proc.320321.208.2013

Summary

The stable isotope records of bulk Eocene sediment at Sites U1331–U1333 are intriguing but complicated. First, they are necessarily incomplete because some depth intervals contain no carbonate. This is especially true at Sites U1331 and U1332. Second, the absolute values of δ¹³C and δ¹⁸O differ from bulk carbonate records constructed at other locations. Upper Eocene sediment at Site U1332 has δ¹³C values that are anomalously high relative to similar-age pelagic sections. Sediment at all three sites has δ¹⁸O values lower than corresponding records generated elsewhere. Conversely, certain features and intervals in the isotope records appear correlated to records at other locations and may provide important information concerning the paleoceanography of the equatorial Pacific during the Eocene.

At least five future tasks are required to fully understand our records:

1. The samples should be placed onto a current age model so that detailed correlations to other sites can be made. That said, records at many other sites (e.g., Shackleton, 1986) remain on antiquated time scales and are only being updated slowly (e.g., Dickens and Backman, 2013)

2. Sample resolution should be increased across certain intervals. As evident from work across some intervals of the Eocene (Cramer et al., 2003; Bohaty et al., 2009), the variance in δ¹³C and δ¹⁸O may reflect time-dependent changes in the composition of bulk carbonate rather than scatter in analytical data.

3. The origin of anomalously high δ¹³C values in middle to late Eocene sediment at Site U1332 (and perhaps some corresponding intervals at Site U1333) should be determined. The values are reproducible but do not make sense with current information.

4. High-fidelity carbonate records should be generated to accompany the stable isotope data. Often significant changes in bulk stable isotopes correspond to changes in carbonate content (e.g., Coxall et al., 2005; Bohaty et al., 2009; Leon-Rodriguez and Dickens, 2010).

5. Other records that might constrain various parameters through this complex interval should be constructed.

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