IODP Expedition 320/321 Scientific Prospectus

doi:10.2204/iodp.sp.320321.2008

Scientific objectives

The PEAT science program is designed to achieve an age transect along the Pacific paleoequatorial region that spans the early Eocene through middle Miocene periods. Time intervals that were covered by previous ODP legs will be integrated with the current transect's results in order to achieve a nearly complete time series. Drill sites target specific time slices of interest (Fig. F5) at locations that provide optimum preservation of calcareous sediments (Figs. F1, F4, F6, F10). The overall aim is to obtain a continuous well-preserved sediment section that will address the following primary scientific objectives (of equal priority):

To document the nature of calcium carbonate dissolution and changes of the CCD over the Cenozoic;

To determine the evolution of paleoproductivity of the equatorial Pacific during the Cenozoic;

To validate and extend the astronomical calibration of the geological timescale for the Cenozoic using orbitally forced variations in sediment composition known to occur in the equatorial Pacific;

To determine temperature (sea surface and benthic), nutrient profiles, and upper water column gradients;

To improve, date, and intercalibrate bio- and magnetostratigraphic datums at the Equator;

To improve constraints on the motion of the Pacific plate and the Cenozoic equatorial region, primarily using paleomagnetic methods; and

To make use of the high level of correlation between tropical sediment sections and existing seismic stratigraphy to develop a more complete model of equatorial circulation and sedimentation in the Pacific.

Additional objectives include the following:

To provide information about rapid biological evolution and turnover rates during times of climatic stress;

To improve our knowledge of the reorganization of water masses as a function of depth and time, as our strategy also provides a paleodepth transect (Fig. F4);

To develop a limited north–south transect across the paleoequator, caused by the northward offset of the proposed sites by Pacific plate motion and providing additional information about north–south hydrographic and biogeochemical gradients;

To obtain a transect of MORB samples from a fixed location in the absolute mantle reference frame; and

To use a transect of basalt samples erupted along a flow line in similar environments to study low-temperature alteration processes.

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