BIOINDICATORS OF DEEP-TIME HEAVY METAL TOXICITY: TESTING THE END-PERMIAN HEAVY METAL TOXICITY HYPOTHESIS

The end-Permian mass extinction coincides with the eruptions of the Siberian Traps, a Large Igneous Province, that passed through carbon-rich sedimentary rocks, with both factors causing a massive injection of large volumes of greenhouse gases into the atmosphere that are hypothesized as causing the end-Permian mass extinction. Volcanic eruptions and the combustion of carbon-rich sedimentary rocks, however, also produces heavy metal emissions, and associated high-abundances in mercury concentrations at the end-Permian mass extinction has led geochemists to hypothesize that heavy metal toxicity also played an important role in the end-Permian mass extinction event. Toxic metal poisoning is, however, only recorded as occurring at the same time as the extinctions and has not been shown to have been biologically available during the end-Permian event, thus it is not known if it had a direct impact. Here, we investigate if well-preserved foraminifera, which are used in modern-day marine ecosystems as bioindicators of heavy metal pollution, from the Permian/Triassic boundary in Svalbard record morphological abnormalities consistent with toxic metal poisoning. Our results show that benthic foraminifera do not record any morphological abnormalities, suggesting that heavy metals did not reach toxic levels at the Permian/Triassic boundary. Samples that record foraminifera were, however, only recorded at the Permian/Triassic boundary and not during the mass extinction event when heavy metal concentrations peak.