The Platycopid Signal of oxygen depletion in the ocean: A critical evaluation of the evidence from modern ostracod biology, ecology and depth distribution

The use of relative abundances of filter-feeding platycopid ostracods in estimating past levels of dissolved oxygen in the ocean (the “Platycopid Signal Hypothesis”) is examined, paying particular attention to evidence from faunistic, biological and ecological studies. The degree of support for the hypothesis has been overstated; available data on ostracod depth distribution show that previous claims for platycopid dominance in the Oxygen Minimum Zone in different oceanic regions are misleading and based on only a few studies. Observations and experimental studies on living platycopids are limited in scope and should be treated with caution. We conclude that previously published and widely applied calibrations of platycopid abundance against dissolved oxygen levels are inadequately justified by the available data. Any further application of the Platycopid Signal technique should necessarily address these criticisms.