Abstract

We have analyzed variations of foraminifera and planktonic 18O in a core from the stable central waters of the North Atlantic gyre. The record of low sedimentation rate (1.2 cm/103 yr) covers 18O stages 2 through 6. Results indicate a 1.75‰ variation of 18O over the glacial cycle. This value is comparable to previous estimates from benthonic records of high sedimentation rate. The general shape of the 18O record also agrees well with patterns derived from cores showing higher sedimentation rates. The low degree of record modification by bioturbation may reflect the core location within the low-productivity region of the subtropical gyre; low delivery rates of organic matter to the seafloor should support smaller populations of burrowing organisms. Documentation of the standard 18O record in a low-sedimentation-rate province indicates that geographic regions where the planktonic 18O record is dominated by the ice volume effect can be extended from the equatorial to the subtropical oceans. Although both regions are characterized by temperature stability, there is a greater annual range of temperatures in the subtropics. These results therefore suggest that covarying benthonic-planktonic 18O changes in Tertiary records can be interpreted primarily in terms of ice volume changes over a broader range of conditions than has been previously proposed.

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