Vast Neogene laminated diatom mat deposits from the eastern equatorial Pacific Ocean

THE eastern equatorial Pacific upwelling region is responsible for up to 50% of global 'new' production 1 and is regarded as a barometer of ocean change. Here we report evidence, from several sediment cores in the region, for repeated episodes of increased equatorial primary production between 15 and 4.4 million years ago, on a scale that is undocumented in the modern ocean. Mats of the diatom Thalassiothrix were rapidly deposited as successive laminations at rates exceeding 10cm per thousand years; mat deposits can be correlated for distances of more than 2,000 km. It is surprising that the laminations were preserved at all: conventional models suggest that bioturbation caused by the benthic sediment community will disrupt such laminations unless there is insufficient oxygen in the water to support the biological activity. In this case, however, the strength of the mats and the scale of their deposition may have overwhelmed the benthos, so that the laminations were preserved by physical means. These remarkable deposits provide a unique window into the Neogene tropical ocean–climate system, and should enable quantification of ancient deep-sea fluxes and the study of short-term (sub-Milankovitch) variability in the ocean.