ODP Leg 138 in the eastern equatorial Pacific (EEP) provided a unique opportunity to understand the paleoceanographic significance of seismic reflectors in this climatically sensitive region. Carefully offset multiple cores were spliced into a complete stratigraphic section for the upper 250 m at each site and accurate, astronomically tuned time scales were generated from these composites. Well log data provided a means to correct composite depths to true depths as well as density and velocity data for the generation of synthetic seismograms. These synthetic seismograms were used to determine the paleoceanographic significance of regionally traceable reflectors by linking variations in the core record to the seismic record. The EEP reflectors are due to changes in carbonate content, primarily due to variations in surface productivity, as indicated by the presence of mats of the upwelling diatom Thalassiothrix longissima. The EEP composite GRAPE records were successfully used as a tuning target for GRAPE records in the central equatorial Pacific (CEP), as a means to detelxnine the basin-wide extent of EEP reflectors, and as a guide to the further interpretation of the CEP seismic record. It was found that EEP reflectors R3-t, R5, R6, R8-b, and Site 844 reflectors R 10, R 12-b and R 13, correspond to reflectors i n the CEP. However, some of the CEP reflectors, which were postulated to be due to periods of enhanced dissolution, also con'espond to diatom mats, and hence the origin of these reflectors must be reconsidered.


Center for Coastal and Ocean Mapping Affiliate

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Geophysical Research Letters



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