the significance of animals stirring up mud

Makes the point that bioturbated sediments, ancient and modern, retain more organic phosphate per unit organic carbon than do non-bioturbated sediments (due to microbial polyphosphate sequestration in the oxygen-exposed sediments that result from bioturbation). Because bioturbation evolved at a definable point in time during the early Cambrian, this implies the origin of a concurrent phosphate sink. This in turn implies an oxygen decrease, because oxygen is produced by burial of reduced organic carbon, production of which is limited by phosphorus over long timescales. The oxygen/phosphate decreases were quantified relative to other relevant parameters (weathering, CP ratio of non-bioturbated sediments etc), and a feedback loop was suggested whereby the oxygen decrease induced by bioturbation is self-limiting, because bioturbation-causing animals require oxygen.



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