Bioturbation has a limited effect on phosphorus burial in salt marsh sediments.

It has been hypothesised that the evolution of animals during the Ediacaran-Cambrian transition had a major impact on atmospheric O₂ and CO₂ concentrations. The models upon which this hypothesis rests, critically assume that bioturbation by the newly evolved fauna increased the burial of organic phosphorus (P_org) within the seafloor, relative to organic carbon (C_org) and that inorganic phosphorus (P_inorg) burial was not affected by bioturbation. This assumption is centrally based on data compilations from marine sediments deposited under oxic and anoxic bottom waters. Since anoxia excludes the presence of infauna and sediment reworking, the observed differences in P burial are assumed to be solely driven by the presence of bioturbators. This reasoning however ignores the potentially confounding impact of bottom water oxygenation on phosphorus burial. Here, our goal is to provide a field verification for the idea that bioturbation increases the relative burial of organic phosphorus, while accounting for bottom water oxygenation. We present solid-phase phosphorus speciation data from salt marsh ponds with and without bioturbation (Blakeney salt marsh, Norfolk, UK). In both cases, the pond sediments are exposed to oxygenated bottom waters and so the only difference is the presence/absence of bioturbating macrofauna. Our data reveal that both the C_org : P_org ratio of buried organic matter and the rate of P_inorg burial are indistinguishable between bioturbated and non-bioturbated sediments. The absence of a clear effect of bioturbation on total P burial implies that previous studies may have overestimated the impact of the rise of bioturbation on atmospheric O₂ and CO₂ concentrations in the early Cambrian. [ABSTRACT FROM AUTHOR]