Measurements of combustion oxygen demand (COD) in two sediment cores provide a record of paleoproductivity driven by surface-ocean dynamics in the equatorial eastern and western Pacific for the past 400,000 years. The COD time series are well correlated with each other over this time span and show pronounced precessionally forced peaks of higher productivity during globally colder periods. The phase of this signal in the two cores is identical, to within chronological uncertainties, suggesting a common insolation forcing mechanism for the upper ocean across the equatorial Pacific. COD is also in phase with the precessionally forced component of global ice volume, as indicated by oxygen isotopes, and with atmospheric methane in the Vostok ice core. These relationships imply that the COD relative paleoproductivity index provides an important diagnostic measure of the mechanisms of tropical ocean dynamics and climate change.