Paleoclimate
Lime mud records Toarcian ocean acidification
Open access · cc by · source: Europe PMC
Micrite boron isotopes from Spain and Portugal show a transient pH drop at the Toarcian Oceanic Anoxic Event that brachiopod shells miss.
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Lime mud records Toarcian ocean acidification
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Atmospheric CO2 rose from about 260 ppm to as high as 1000 or even 1800 ppm.
This led to a rapid elevation of atmospheric carbon dioxide (CO 2 ) concentrations , , from ca. 260 ppm to as high as 1000 ppm or even 1800 ppm , then a return to pre-event values , .
The T-OAE interval lasted about 500,000 years.
This interval has been recently calibrated to last about 500,000 years consistent with the timescale for CO 2 removal by enhanced silicate weathering .
Key findings
Micrite δ11B fell by about 4–6‰ at the negative carbon-isotope excursion, tracking modelled surface-ocean pH decline to just above 7.4, while brachiopod and bivalve δ11B stayed nearly flat. Faunal stress coincided with low pH, but community recovery did not require pH rebound.
Methodology
Authors measured boron, carbon, and oxygen isotopes in micrite, rhynchonellid brachiopods, and oyster bivalves from two NW Tethys carbonate sections, screened samples for diagenesis, and compared the records with a COPSE carbon-cycle model of ocean pH.
Limitations
There is no modern δ11B–pH calibration for micrite, so absolute pH values remain model-dependent. Brachiopod buffering and a data gap in the lower T-OAE limit a statistical kill-mechanism test, and Spain and Portugal recover on different timescales.
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