Climatic cyclicity at Site 806: the GRAPE record

Abstract

We used the continuous saturated bulk density records collected by the gamma-ray attenuation porosity evaluator (GRAPE) at Ocean Drilling Program Site 806 on the top of the Ontong Java Plateau to evaluate the continuity of the recovered cores and to splice together a complete section from the multiple holes drilled at the site (for the upper 165 m, this is equivalent to approximately 0-5 Ma). The GRAPE (saturated bulk density) changes at Site 806 are the result of changes in grain size, with density decreasing as grain size increases. We attribute this to the removal of fine particles by winnowing, leaving a greater percentage of large hollow foraminifers behind - "the winnowing effect'. We suggest that the winnowing signal is a response to increased thermohaline circulation and benthic storm activity associated with enhanced north-south thermal gradients during times of climatic degradation. -from Authors